The seat motors and track assembly are replaced as a unit. I have attached a description of how the power driver seat operates, the overview diagnostics and detailed diagnostics to determine the cause of your problem, and the procedure to replace the motors and tracks as a unit.
It appears your problem could be the seat switches or the motor grounds, or the seat motors or the tracks. Seat switches arc and get damaged over time, so that is a strong possibility. The grounds for the motors may get rusted and fail so those should be tested first and second in my opinion.
Good luck.