Quit few numbers of 993 steering racks are starting to leak out here, the leak is generally very minor leaks around the rack seal area.  It does not cause any steering malfunction unless the reservoir is drained of the fluids, which means if you are suffering a steering race leak you will need to check your power steering reservoir often.  Since the leaking area is covered by a protective rubber boot the leak is generally not noticed until a much later time when the power steering fluid actually eats through the rubber boot and cause it to crack. 

There are few places that offers remanufactured 993 steering rack for sale, you can easily find these places on line by doing a search for "993 steering rack" in yahoo search.  After doing some telephone inquiry I found out that a remanufactured 993 steering rack costs around $450, and the core charge is anywhere from $150-$350.  Just out of curiosity I checked with the local Autozone and found out that they also sell a remanufactured 993 steering rack for $455 ($150 for core charge), so I just decided to buy it directly from Autozone to take advantage of their life time warranty. 

During the same time Hank was researching a steering rack for his 993 RS project and found that the 993 RS steering rack is a steering rack from a 964 unit part number 964 347 009 04.  I am not sure if this information would be helpful, but I have been told that the 964 remanufactured steering racks are considerably cheaper than the 993 units.
 

Remove driver's seat (This is optional, it will give you more room to work with under the pedal cluster area if you remove the seats)

Remove pedal cluster floor board.  Go to this DIY for the floor board removal instructions.

Jack the front of the car up and placed on jack stands and remove the front wheels.  Go to How to jack the car up for front jacking instructions.

From the center position of the steering wheel turn the wheel until the steering shaft universal joint bolt is exposed in a position where you can get a socket to loosen it.  Once the bolt is removed you will need to tap a chisel of a flat screw driver into the split opening of the spline clamp and tap the universal joint upwards to make sure that the spline clamp can move freely.  (Example in right hand side picture) But you do not want to remove the spline clamp from the shaft at this time, because you will need to turn the steering wheel in later procedures. 
  

Unbolt the 10mm bolts from under the front plastic pan and remove the pan

 

Unbolt the tie rod bolt on the left and right side hub.

Use a tie rod remover to push the tie rod out from under the hub on each side of the car.
    

Loosen the tie rod locking bolt (when loosen the locking bolt you will need to use two wrench to prevent putting pressure on the steering rack)

Loosen the tie rod from the ball joint (count the exact number of turns it takes for the tie rod to comes off.)  My count was 18 on each side.  

Slide the rubber boot off the ball joint and loosen the ball joint (Also using two wrench at the same time)
 

Unbolt the hydraulic feed and return line (17mm) on top of the steering rack unit from under the car. (Difficult to get to)  At this time you want to have some rags and a drain pan ready because as soon as you loosen the bolt the power steering fluid will come pouring out.   Also have something ready to cap the lines with.  I used the cut off finger section of my latex glove tied with a wire tie.  (It's messy!)  Be careful not to loose the brass seal rings when you remove the hydraulic lines.  There are two brass rings on either side of the line connector on each line.
   

Remove the 4 allen steering rack mounting bolts.  

Did not have a chance to take any pictures during these following procedures, so you will just have to use your imagination.

Have someone turn the steering wheel all the way to the right, and drop the steering rack on the right side down first.  Once the right side have cleared, turn the steering wheel all the way to the left so that the left side of the steering rack will clear the cross member and drop down.  

Once the old steering rack is out you will need to swap over the mounting rubber/metal bracket and the hydraulic line holder bracket and boot over to the new rack.
 

When I removed the rack I made a mistake of taking off the complete steering column universal joint with the rack.  The reason why it was a mistake was because it was very difficult to reinstall the universal back to the steering shaft correctly.  But it did help me in positioning the steering rack arm in proportion to the original position prior to installation, so that I only had to do a very minor adjustment of the steering wheel to center it back. 

Reinstall the steering rack left side up first and line up the spline shaft with the spline clamp from the top side and then once the spline clamp is secured turn the steering wheel all the way to the right side to get the right side of the steering rack up. 

Install the steering rack mounting bolts just hand tighten.  Only one side of the steering rack bracket touches the cross member of the frame, so you will need to tighten those bolts first so that the mounting bracket almost touches the cross member, and then tighten the longer bolts on the opposite side until they bring the bracket up evenly.  And then go back to tighten the bolts on the cross member side to 45 Nm, and then the long bolts facing the front of the car also to 45 Nm.  (The factory shop manual recommends that the steering rack mounting bolts to be free of debri and oil when it is reinstalled, also now it would also be a good opportunity to perform the TSB on the steering rack bolts on earlier model 993s, it also states to replace the bolts once they have been removed.)  

Install the feed and return hydraulic lines tighten to 20 Nm.

Under the left side of the steering rack gear box you will find a hole that either have a black rubber plug on it or has been filled with some sort of silicon on a remanufactured rack.  Remove the plug so you can observe the steering rack centering hole.   Now you need to turn the steering wheel so that you can see a dimple through the pilot hole.  Once the dimple is lined up with the pilot hole you know for sure that the steering rack is at the absolute centered position.  There is a taper head bolt that is used to lock in the center position of the steering rack, I didn't use it during this DIY because I didn't have access to that special bolt.

Now is time to center the steering wheel.  Disconnect the negative terminal of your battery.  Remove the two torx T30 bolts behind the steering wheel on each side to remove the air bag, (The factory shop manual recommends that the air bag bolts to be replaced each time they are removed.) disconnect the air bag and place it with the padded side facing up.  Remove the steering wheel bolt and and spring washer.  The wiring connection behind the air bag works like a spiral spring "Coiled contact unit", it will allow only so much wind-up in each direction.  So it may be damaged if it is not reposition to relieve the tension from the incorrect position of the steering wheel. The 993 steering wheel assembly have a device that automatically locks the "coiled contact unit" when the steering wheel is pulled back.    To center the "coiled contact unit" properly you will need to place the contact unit in the end stop position.  Starting from end stop position, turn back contact unit by two turns and continue turning to the center position mark.  The exact center position is indicated by two arrows in the picture below #1.  Once the "Coiled contact unit" is centered you can now mount the steering back.  After centering the steering wheel, install steering wheel bolt tighten to 45 Nm, air bag, and air bag bolts (10 Nm), and then connected the negative terminal of the battery.
  

1. = Center position mark (arrows), 2. = Driver's engaging into the steering wheel, 3. = Lock (rotation lock) becomes effective after removal of the steering wheel.

Reinstall the ball joint tighten to 70Nm and install rubber boot, replace any cracked boot.  It will help with the installation of the rubber boot if you use some grease on the lip of the boot.  You will need to slide on the rubber boot first and then have someone else turn the steering wheel to either direction so you can get enough access to slip the boot over the locking lip.  (Very frustrating process that took me over an hour!)
  

Install tie rod  and count the numbers of the turns that you wrote down when you first removed it.

Tighten the tie rod locking bolt to 45 Nm.

Install the tie rod back into the hub and tighten the tie rod hub bolt tighten to 75 Nm.

Install the steering column universal shaft spline clamp bolt and tighten to 23 Nm (Factory shop manual said to use new bolt)

I then test the system for leaks prior to installing the front pan back on the car.

Here is the procedure to bleed the power steering system:
Fill the reservoir with fluid, start the engine briefly and then shut it off, and fill the reservoir again, do this until the reservoir fluid level does not fall rapidly anymore.  (Never to allow reservoir to drawn empty)  let the engine idle and turn the steering wheel several times rapidly from stop to stop to allow the air to escape from the cylinders.  Check the fluid level again while the engine is running to get the correct level reading.  

Reinstall the front pan, and then the front wheels.  Lower the car and you car done!

(It is recommended that you will still need to get the front toe-in checked on an alignment machine just to be sure)