99 e class rear window regulator
 

What is it that breaks on these ? The window will go up and stay up by lifting by hand but the motor just makes a click noise like the window is allready up. I mean what part of the regulator ?

The part that holds the sliding jaw to the track breaks, and kind of rotates when it breaks so the sliding part is all the way up like normal, but the window is physically lower. The motor thinks everything is fine (which actually it is) but because of the broken part the window is lower than it should be. That's the kind of failure YOU have, pretty common. There is another type of failure when the window isn't moving at all, that's a pulley that snaps off at the top of the regulator, or actually the bracket that holds the pulley to the regulator. When that happens the window is all the way down. The pulley redirects the steel cable from the motor, up to the top of the regulator and back to the motor.
Gilly