I had this problem several weeks ago. Posted a question, but no one responded. The MB shop manual and everything else I've read say the first step is to lower the window. How if it's stuck?
After removing the door liner and weather proofing you will find that there are 5 bolts which secure the window regulator. Two secure the regulator arm which is used for adjustment. They come off easily. The other 3 secure the motor side. I found that they had immense pressure on them and could not be moved after taking off the nuts. (Notice that if you hold the switch in after window reaches the top the door will bulge out towards the inside of the car). I put the nuts back on the ends of the bolts and managed to knock two of them in with a hammer. At that point the pressure was released enough for the regulator to lower a little. Guess what? I tried the switch and the motor brought the window down. Put everything back together and it has worked fine since, so maybe you don't even need a new motor.
Oh yeah, remember to secure the window at the top with a wedge or duct tape before you remove all 5 bolts or it might come crashing down. Lots of sharp metal in there--don't want to lose a finger.