Saw this in another forum:

Concerning MTX-5 gear stripping problem, MUGEN have investigated and tested at different tracks to solve this problem in Japan.
Finally we have found out that the cause of 2nd gear stripping problem was in the rear urethane belt and not in the 2nd spur gears itself or whatever.
In order to solve this problem, you just need to replace the rear belt from urethane (T0266) to rubber belt (T0269).

http://www.rckws.com/discuz/forum.ph...extra=page%3D1