My Sand Shark stopped working. I have replaced it with a robot, but would like to get it functional if possible so I can sell it. The symptom is that it no longer moves, even with high suction. If I look under it while the pump is running, the thing that normally clicks back and forth is stuck one way and the water just flows past. Looking at the exploded views on line, I don't see anything obviously missing, or broken. Any suggestions would be great, thanks.