I have a 2006 YZ450F that broke the shaft part of the 2nd gear shift fork, this is the second time. I split the cases and the only thing that looked bad was the the shift fork, the gears looked good etc etc. I replaced the shift fork, bench tested it and everything seemed good........but 3 rides later the excat same thing happened again. Once again I have the cases split and looks like the only problem is the brokes shift fork shaft....anybody see anything like this before?? any suggestions??