1992-1994 W140s S class cars had a defective part that attached the glass of the window to the control arm that raises it and lowers it.

This part is plastic and not very strong. The result: after regular use the part eventually brakes and has to be replaced by a newer designed part fitted to 1995-on models.

Seen this happen in several W140s and usually the rear door windows tend to give more problems than the front.

The only way to solve the problem is to access the control arm and change the plastic link.

Good luck!

A. Rosich
S320, 1998
E320T, 1995