The reason why…
My 993 Carrera 2 was upgraded with a Carrera S spoilergrille. (original part number 000 044 800 98). Unfortunately the grills as well as the centerpiece were not correctly installed by the previous owner. Result: I lost the right grille driving around 130 Mph

 
Oeps… 
The centerpiece was not installed correct as well….

 
 
I ordered the original grill (993 512 587 01C) as well as 10 clamps (999 591 390 02 ) and the adhesive kit (999 915 509 40)
 

 

It is easier to do the repair while the spoiler itself has been dismantled completely. This allows also to check the mechanism. 
For removal please check: http://p-car.com/diy/aerokit/tailremove/tailremove.htm
 
 
Check the retrieval mechanism on corrosion and repaint the small rolling bar (dotted line in picture)

 
 
Remove the old kit layer very thoroughly with an abrasive or grinding tool.
Especially the edges on the left and right side are used to create a strong connection between the grill and the spoiler. 

Just rework the edges (left and right) with an abrasive tool or abrasive paper (180)
 
Next step is to clean the complete inner edge of the frame; this is mandatory for a good seam or suture

 
The enclosed primer will form a base-layer for a strong connection.  
Be careful ! This black primer can make stains on your paint that will be difficult to remove.  Be sure to “paint” the primer just below the top of the edge. This will cover up any kit- left-overs that will arise when the grill is pushed into the frame 
 

 
In the background you see kit component A, component B and the accelerator.

Hint:
Officially you have to follow the guidelines within the Porsches Repair Manual and probably it requires a special kit-pistol to mix and bring on the kit.

You should use as much component A as B but just a few drops of the accelerator. I did mix it manually (lack of special tools) and remind that during mixing the temperature is going up which is speeding up the harden-process. 

 
Place the grill carefully on its place and push it in the frame.
Wait 15 – 30 minutes for the kit start to harden

Next step: mount the clamps cross-wise. Push the grill firmly into the frame and press the clamps as tight as possible. Use a small screw driver.
 
 

Check on any stains or large kit left-overs and remove if any.
Let the kit harden for around 24 hours

Remove the kit the is sticking outside the grill. Don’t forget the backside !

 
Alignment of the spoiler

A : To align the retrieval mechanism with the hood filling plates are mounted.
This is done in the factory so should be OK but you can also position the spoiler into the hood itself 
 

B / C
Micro switches have small thread ends which determine the up and down position of the spoiler

D:
Check if small toothed wheel is not set too tight
 

And ready
 

 
 

The complete repair took me 8 hours (hardening time excluded) but with this manual you should be able to do it faster.