I have a 78 300D and my windows are starting to drive me CRAZY!
In perticular the rear windows and the front passenger window. What I see happening is that the aluminium struckture(sp?) that holds the motor and the arm that raises the windows is bent. I replaced the rear aluminium assemblies and straightend them out, but within a couple of weeks they were bent again. An easy way to tell if they are bent is that the window will grind/make clicking noises when it reaches the top.
Does anyone know if ther are updated assemblies that do not bend? I noticed that my parents 83 300td does not have any problems what so ever with the windows.