I'm guessing your regulator is bent a little. All the moving parts have lost their grease and don't move as easy as when new causing the regulator to get too much torque on it. Easy to get to and replace or fix. If you do, there are threads here to help with removal of door panel. I have not had to do it with my W126 but I know on the W123's I have done, there is a trick to getting the map pocket off.