"the motor runs but the seat doesn't move"
I had the same thing happen to me. The problem was the speedo cable that connects the motor to the gears that move the chair wasn't seated right. In fact one of the ends was kind of bent out of round. I flip-flopped the cable and it worked again. You might want to try this too. If not you might need a new cable. I doubt the gears are stripped.
You will need to completely remove the chair to do this by the way. I found a bunch of stuff under the seat too.
