Power windows 1972 911s coupe

Hi,
I have a 1972 911S coupe with power windows. The windows are very fast, scary in fact, and really hit on opening and closing. On occasion the passenger window gets stuck in the down position. The problem seems to be the window sneaks past one side of the rubber stopper affixed to the door, which is meant to act as a stop, and and the window gets stuck next to the rubber block, wedged in. If the window was not moving so fast, it would not wedge itself in. Most of the time I am careful with it. The last time it got stuck was in December, but I would love to find a fix for this. Am I missing a part? Is the spring wound too tightly?
Any advice will be greatly appreciated.
Post or PM me.
Best,
Marc