My friend has what I believe to be an M-21 4 speed, it has a 10 spline input, but it has a bad 2nd gear synchro. It grinds badly on every shift into second gear. Anyways, I would like to know if this is something I can do with basic tools or should I take it to a pro? I am not affraid of transmissions, I have rebuilt a motorcycle transmission that a local dealer had broken twice before.