For me, it would be hubs and spindles, both come in the same package, coincidence? After that, the only other thing that gave me any real problems was the stock diffs. Anything else I broke was due to a bad crash. Lost a rear dogbone the other day after doing a few kart wheels, but due to pure luck, the tie rod for the rear suspension only popped off and even more luckily, the dogbone landed about a foot away! Not too bad for a 3/4 speed kart wheel. Never broke any suspension arms, but I did bend the stock hinge pins. Replace them if you haven't already, they are worth every cent to me, both smoother suspension travel and alot tougher. And one other thing you may want to get a replacement for, the body. Of course I had a dog help mine to oblivion ( this was a result of the failed rear diff by the way, had they been good, coulda ran circles around those dogs) Other than that, the mt2 has been pretty reliable for me. Guess it depends on the driver and maintenance.