I think that the regulator may be getting stuck. Tke the door panel off and make sure that the cable is aligned and that the regulator is fine, otherwise just leave it alone.........as long as it goes up and down you're fine, right? If there is a bigger problem its bound to happen regardless so if it ain't broken, I say leave it be, or be prepared to replace a possible $250 part.....but at least its only a 30-40 minute job.

__________________

1990 190E 3.0L