Long shot but check the convenience relay. Under the rear seat drivers side. You can remove the cover hook it back up and you'll see which relays supply power to that window when you press the switch. If you think that's the issue you can try and clean the relay by bending the braided wire and pulling away the small metal piece then lightly file it. And to remove the relay the middle tab by pulling it out the two side connectors unlatch by pulling the piece to the side.