A few years ago, Mercedes advised that both front window motor need to be replaced at $300 plus per motor. Any way to remove and rebuild these? Kinda like an old Sears drill?

To the best of My knowlege no one on the Forum has done what I would call a compete rebuild of the Motors and that is likely why you got no specific answer on that.

People have gone into them and replaced Brushes freed up parts and relubed them and a vagely remember someone adding a washer to take up some end play.

There used to be 2 threads that had pictures of the Motors taken apart.
That info is likely in the below Repair Links:
Fast navigation http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html

Please note that to me a complete rebuild is where you take something apart and when you are done you have replaced all the out of spec parts with new ones and the Item is expected to perform like a new one.

Other then the Brushes I am guessing other parts of the Motor are hard to get.
There also might be some Companies like Cardone that rebuild the Motors.

I am not sure what info is on the other Forums like Benzworld.org or the Mercedes Benz Club of America. They may have more info. Othere Members might have more info on what the other forums have to say.

Also if a Motor is bad a lot of people simply replace with a used one from the Junk Yard or buy a used one on eBay or from one of our Members.

__________________
84 300D, 82 Volvo 244Gl Diesel

Very helpful! Thank you.