why does my power window motor arm continue to fall off the track when rolling up the left rear window?

My 2002 Toyota Highlander is unable to roll down either rear door power windows. It was my daughters car. She has three Husky dogs she used to carry in the back. It is presumed the dogs knocked the rear windows off the tracks. I can hear the motor working but it does not move the windows.  In taking off door panel, motor arm is resting under window.  I reaffixed arm to track, but powering window up, it came off again.  sprayed silicone on rubber but it came off track again.  What is the problem? Motor?