I have a sheared screw in one of my rear door covers. It's a T8 head #4 screw. You can cut the insert off with a razor blade, and a new one is part# (below) and it's $3.40 at a MB dealer, or $6 on ebay from lithuania. From a local parts car and some serious removal attempts, this part isn't really removable. Hopefully this will help someone, took a while to track this part down.

A1236900018