[kenikh]

That's some gnarly carnage - a question, then a guess:

Does your track happen to have an ascending acceleration zone where you redline shift from 2nd to third, then carry third through the fattest part of your torque band?

My guess is that your high HP/torque motor finally had its day with third gear. The power pulses from the big part of the torque curve, likely with the wheels highly loaded (e.g. up a hill) likely were pounding free play into the interference zone between the shaft and gear. Once that free play hit a ciritical juncture, all it took was one more hit to third gear to spin it loose.

I believe that this is why the VW guys weld their 3rd/4th gear hubs when their transaxles are used in high power applications - it helps keep things from coming loose and raining destruction on the gearbox (at least for a while).