I would check to see if a wire got cut. I thought on my Grand Prix I had a bad motor but once I pulled the seat and removed a flip flop and a bunch of other trash the previous owner jammed up under the seat I found 2 of the wires where broken. I fixed them and all has been well.
Now on the FB Vert there was just too much to deal with to fix on it's power seats, so I pulled the track and got a manual track from the salvage yard and I can live with it.