The window status is as follows,
The car was brought to Mercedes for other issues. The service tech looked into the window problem and said the motor was bad (again) and needed replacement. I did not bother to do that because it was a seldom used rear window. Around a month after that, the @$#^%^% thing started working OK! No new proceedure was tried. It just started working.
So you could say that is an ending without cause.