To the community of car enthusiasts and all Golf III drivers suffering from door squeaks.
If you're experiencing squeaking noises in or around your doors, you should try the following before completely disassembling the door.
While driving very slowly on a bumpy road (and potholes are a rare but welcome occurrence), open the relevant door slightly to see if the squeaking disappears. If it does, you can be fairly certain that the plastic piece on the corresponding latch is worn out (even if you don't see any visible wear on the part!). The part number is 1H0-837-034-C and costs €3.31.
After buying a used Golf 3 GTI TDI, I searched for a long time to find the source of this squeaking noise. Nothing I tried to lubricate on the lock or locking mechanism worked. For 3 weeks, I've had two new locking wedges on both sides, and I'm happy about the peace

.
It took me a while to consider the possibility of a shim, as I previously owned a Golf II 16V where the plastic sleeve on the locking pin was severely worn, yet it still didn't make any noise.
Greetings from the North Sea.
Andy.