Harold, I blew out my input shaft gear and a few teeth off first and second in my M20 a few years ago. Had to source some new parts and a rebuild kit. I'd never done one before but it's not like an automatic, like magic or something. Pulled it apart and put it back together with the new stuff. It wasn't that difficult. Seems like there was some issue with the reverse shaft and gears had to go in at the right time. My other concern was I didn't put any sealer on the countershaft before it went in. All that said, it's been on the shelf for about eight years now because the replacement Trans I bought till I got my original done works fine and I see no reason to change it out until I need to. So I really have no idea if I did it right or not.😎 Never hurts to have a spare laying around though.