I would not buy used TA or attempt to rebuild them yourself. New gears alone won’t fix the problem. The electronics also go. I bought 2 used ones and rebuilt them and my originals with new gears. They all failed eventually. I wasted a lot of time changing them and a few hundred dollars. Buy new or rebuilt. Abdul at Mpower Motorsports sells rebuilts with a lifetime warranty for $360 each.
https://www.mpowermotorsports.org/