Just spotted this so I thought I would pass this on.
I had both my motors go on my Polo, it always happened in the cold weather and the window just stayed closed. I bought a replacement for the first one at around £110 (I think) and fitted it myself. When the other went I loosened the motor to gearbox screws whilst still fitted to the car and it started working.
It ran all summer then stuck again in the winter. This time i unbolted it but left it connected to the power and carefully pulled the motor drive from the crank casing about half an inch and run the motor briefly to move the spindle. I put it back and it ran for another 6 years till I sold the car.
The new replacement also failed after 4 years and I did the same again. This time drilling some extra holes in the door to allow easier access to the bolts..
I think its because they always stop in the same place and wear on that rotor, by turning the motor spindle it stops in a different place.
Worth a try if your going to change them yourself anyway, might save a few quid.