Here is a picture of the old and new kinematic lever

According to the 993 factory shop manual, the solution to fix the clutch pedal not fully return problem is to replace the kinematic lever in the clutch assembly.  The newest part number for the kinematic lever is 993.423.519.03, apparently Porsche had a total of 4 different updates for this lever.  Defective part numbers are 993.423.519.00 or 993.423.519.01 (gold color).  The improved parts are 993.423.519.02 or 03 (olive color)

(1). First step is remove the floor board, please consult the following DIY on how to remove the floor board.  (It is optional if you want to remove the seat or not, when this DIY was performed the seats was removed for easier access.

(2). You will need to use a vice grip plier to close off the hydraulic inlet hose to the clutch master cylinder before pulling off the tube, it is connected to the master cylinder by means of the rubber grommet.  You will need an in-line wrench to loosen the nut on the outlet line and pull it off.  * It is difficult to get the outlet line to come up far enough to clear the master cylinder, but it is possible.  There should be little or no fluid to come out of the outlet line, but just to have a rag handy if it does.

(3). Remove the brake pedal clip, throttle clip, brake light connector, and the cruise control signal wire (green wire on the right side).

(4). Remove the 4 bolts that secures the pedal assembly to the floor board, and you can now remove the pedal cluster assembly out from the car.

Note: It is recommended by the shop manual that you mount the pedal assembly in a vise while it is being worked on. 

(5). Turn the clutch servo spring tension adjustment bolt all the way out so that there are less tension on the clutch pedal return spring.

(6). Partially push the clutch pedal in so that the hole on the white plastic spring tension holder lines up with the hole on the side of the frame, so you can insert a punch (drift) to hold the tension spring and release hold the tension off so that the master cylinder can be removed. 

(7). Now you can remove the plunger on the master cylinder by removing the safety clip and then using a pry bar to push the kinematic lever up to give the plunger some slack to be slide out.

(8). Remove the two bolts that secures the master cylinder, and remove the master cylinder

(9). Now it would also be a good time to remove the cruise control switch by loosen the two philips screws.  (You may also want to mark the position of the micro switch prior to the removal to save time on installation position adjustment)

(10). Now use a small flat screw driver to remove the safety clip that holds pin that connects the kinematic lever to the link and also remove the pin.

(11). Loosen the bolt that holds the kinematic lever to the clutch pedal shaft.

(12). Use a drift (punch) to tap out the shaft, leave the bolt loosely threaded on the shaft so that the impact force don't all the sudden force the shaft to fly off in the other direction.

(13). Once the kinematic lever is removed you can replace it with the updated unit.  Notice the notch on the teeth of the shaft and the kinematic lever, when installing you will need to line them up together precisely.

(14). Use the clutch pedal shaft nut to tighten the kinematic lever to the shaft, but do not use too much force.  As soon as the kinematic lever is secure on the shaft then remove the drift (punch) from where you first used in #6  in the hole on the white plastic spring tension holder lines up with the hole on the side of the frame.  And then tighten the clutch shaft bolt to 34 Nm. 

(15). Install the cruise control micro switch back to the pre marked position, you may not want to tighten the philips screws all the way since you may need to adjust it after the master cylinder is installed.

(16). Install the master cylinder again you will need to use a pry bar or to push on the clutch pedal so that the plunger on the master cylinder will line up with the kinematic lever

(17). Tighten the two bolts for the master cylinder, and adjust the cruise control micro switch.  The micro switch must be triggered (clicking sound) on the first few millimeter of the pedal travel.

(18). Set the adjustment screw of the servo spring to the dimension of 6mm.  The 6mm distance is measured from the inner face of the bolt head and the rocker.

(19). Install the pedal assembly back into the car and install the brake, throttle linkage back on and plug in the brake and cruise control connector.  And check for brake light function.

(20). Bleed the system through the clutch slave cylinder.  To see procedure click here.