I think some one is feeding you some BS you can repair the motor, there is How to somewhere I will try find it or you.
I did strip down and clean my motor 6 weeks later same problem again.
I changed just he motor item 2 that's all you need from the link below RealOEM.com BMW R53 Cooper S EL.FRONT DOOR WINDOW LIFTING MECHANISM
There about £85 and it takes about hour and a half to two hours to do.
Longest part is aligning the window but that's easy
Hope his helps
Strip and Rebuild link as promised http://www.mini2.com/forum/first-gen...ing-guide.html