about this issue. Happened to me already. Let me tell you how this thing works. Under the seat, there is a motor with two "in tube flexible wire drives" outgoing, one at each side. Over time, tube seems to stretch making the inner wire loose on the motor, so only on wire is turning, taking up only one side of the seat back. You can remove the guilty tube from the motor, disassemble the tube termination (metal part fitting in the motor), shorten the tube by about half inch, and put it back to the motor. (there are alternate methods, think Bruno’s site has something on this but not sure) Be careful to re-assemble with both seat back sides aligned, or you will have a twisted back all over the reclining range (means you have to align before removing power from the seat).
I did remove the seat from the car to do this job, two bolts, the electrical plug, the seatbelt I think, and a tiny wire that synchronizes the seatbelt height with the seat front/rear location (careful with this last, is very fragile).