[Duncan Macdonald]

Quick fixes that don't involve replacement:
Find a way to cool the motors. (add fans or get a can of compressed gas for in between matches)
Make sure your arm is neutrally balanced to reduce the load on the motors. There was a theory that jaguars didn't work well with window motors, not sure if this is true.
If you are controlling the arm with any sort of feedback make sure the motors aren't continuously running to maintain position. (Add a large deadband)

As others have said, this is what window motors do when under load. Replace them if you can.