I should have taken some pictures, took the damned thing apart more then three times!
I will give you some warnings before you start: be very carefully with removing the C-pillar panel, if you do it wrong the clips that hold it will break. If I'm wright you have to slide the panel forwards and then pull it towards you away from the C-pillar.
You don't have to remove the back seat, but it makes it easier to remove the panel. The panel is tricky; make sure that the silver strip on top stays attached to the panel, it's a ***** to put it properly back in place, if not impossible.
Most likely what broke is a little special "washer" that connects the regulator pivot-arm to the metal parts that holds the window. You can get this at the dealer for $2.50.
I fixed mine, bought a used one from
mercedesdismantlers for $50,- to find out I only needed the $2.50 "washer.
It makes sense to open the good side as-well, so you have an understanding how it all works, to just figure it out will cost you days!
The regulator in the coupe is a complete different story then the sedan, it's not very repair friendly.
Good luck!