1999 Volkswagen Jetta window regulator keeps malfunctioning

I've already replaced window regulator (3X) and motor (2X) in the last 3 yrs. before window stops working altogether : It'll make a rubbing noise when going up and moves slower. When it goes down at times it's almost like free fall. Eventually it'll only go partway up then stop. motor is still working. when door panel removed the cable on the Rt side of the regulator is shredded. Is there an allignment problem that keeps reoccuring or are there some clips or guides missing?? I haven't burnt out the motor yet, but that's next. I just try and leave it alone thx for your assistance.