Window go 3/4 down then Slow
 

I have a 535i 92 and the drivers window goes down 3/4 of the way no problem the last 1/4 is slows to an almost stop if i press the button and let it go several times it will eventually go down all the way (happens even on one touch) but it goes up at normal speeds. I am not sure if its the motor or what else could it be?

Ben