When I bought my '95, the key would insert but not turn the rear hatch lock, which was the same problem I had with my '92. I tweaked the fix here with some updates, but still look at the more complete, original tech article I wrote about this on my '92 TT back in 2003.
From inside the hatch, undo the two 10 mm nuts that attach the lock to the body, then unclip the black electronic bracket from the lock, but leave the black electronic sensor bracket in the car still connected at its white connector.
The black electronic "bracket" above can be unclipped from the lock with the lock still in the car. The black bracket should pull loose without any tools. Do this first while the lock is still in the car.
For the picture above I also removed the black bracket from the car. The main point is the lock is easier to work on without the black bracket clipped onto it.
This was before I cleaned the parts but showed the orientation of the spring at the keyhole.
After the larger round cap was pried off, these three smaller pieces fell out - spring, keyhole flap, keyhole cover.
This is the lock fully disassembled. Removing the small C-clamp shown near the middle allowed the tumblers to be completely pushed free from the housing.
The slots holding the tumblers and are all gunked up from exhaust and road grime. I dropped the entire tumbler into a container with degreaser for a good soaking.
When I did this on my '92 TT, I did not remove the tumblers from the housing as shown above. Do it the way shown here for a more thorough cleaning.
Cleaned and oiled. All the tumblers were moving again. Use a light oil on the tumblers.
These two pieces have to interlock as shown before sliding them back into the housing. Put a light coat of lithium grease on the outside of these parts which have to rotate inside the lock housing.
For reassembly, gently bend the tabs on the keyhole cover so that it snaps into place and does not just “rest” in place. Then it will hold the pressure of the spring underneath.
Reassembling the spring, keyhole "flap" and keyhole cover shown above in place at the end is tricky because the spring is trying to push all the pieces apart. Hold the metal key flap in place with a small screwdriver sticking THROUGH the slot in the keyhole cover above, while at the same time snapping it in place.