Just about everything on the Jetta MKIV is made of plastic, and as a result gets old and brittle. The plastic clip inside the retaining ring for the manual window crank will eventually break if you have to remove the crank a couple of times. This is a replacement. You can see the window crank, and black retaining clip here:
This part replaces the black clip.

This part didn't slice perfectly, but the result still seems to work fine. I ended up making the top wall very thin so that the pin on the crank would slide over the clip, but when it printed the track for the ring went all the way through the wall. I printed it in PLA, and it's a bit too stiff. Printing in ABS might be better.