1999 e320 rear window problem
 

Wife ran all four windows down to vacate hot air inside of car. When she closed the windows, rear passenger window failed.

I pulled door panel off, found two pieces of white plastic, inside the bottom of the door, almost dead center. While they both appeared to be snapped off, they did not fit one another. One very small rounded piece, the other irregular shape 1/4 inch long.

I could not determine where the broken pieces came from. Off of the back of the window motor or someplace off the window register.

Applying upward pressure on the plate glass and operating the switch, I was able to get the window to close. The motor seemed to operate free and clear.

Problem is the window will not stay up, it slides down with every bump.
Anyone have any ideas? I am sure others have had this occur.

Just needs a regulator, very common. Lucky for you they're very cheap and easy to install. Just need to drill out the old rivets and rivet in the new regulator. Do a search, someone will have instructions.