There was (and still is?) a lot of discussion and debate about the root cause of the MTX-4 gear stripping problem. Is it the car or is it the mechanic? I did quite a bit of research on the problem and with the help of a few people, I was able to put together a guide to minimizing the the chance of stripping the gears that was posted on nitrokb.com. ( posted here: http://www.rctech.net/forum/6686934-post3398.html
The are a number of reasons why the gear strips. If you don't understand the specific reasons why gears strip for your particular car - or any car for that matter, you'll never get a handle on the situation. But even with all possible info on the situation, some people still had problems with the MTX-4.
I've stripped my fair share of gears on the MTX-4 and the RRR. In each case, I tried to think about the circumstances of the race; if an accident could have caused the engine to shift, if I didn't check something or adjust something before or after a race - or if I just did something wrong. Whatever the case maybe, there are people that never have problems or can easily pinpoint why their gear strips.
The MTX-4 is an awesome car. I have some personal issues with taking the engine in and out, but other than that, on the track, it's great.
If you can't get rid of the gear stripping problem, changing cars may be your best option for avoiding the problem - because each car is engineered differently. IMHO, it's really about you and the car. Not just the car.