I think ejsharp has the right idea. What I would like to know is there any kind of way to lubricate it without removing the door panel? I am not quite certain due to the fact that both back doors will behave as if off the show room floor one day and other days I have to heave-ho to get it open? BTW it's not the rear door's alignment both are fine. I don't want to spray WD-40 on this track for it might get power window functions covered in it. I have heard of one other owner of a Benz to have the same problem but find it odd that I can't seem to find any other stories similar to mine on the site.