Wow...no pinched fan cables or anything? How long has that one been mining up until that happened? What type of power supply were you using? What's the ambient temp where it's mining?
Sorry for the questions, but I've got 6 that have the 49.9k/50k mod. 3 have been running non-stop 24x7 for 2 months, the other 3 have been running non-stop for about 3 weeks now. When I've modded them, I did add some small heatsinks to the mosfets because a little extra cooling never hurts when overclocking anything.
I suppose repeated high current spikes and overheat may help damage the mosfet, I think those little LFPAK rated for 76AMP might be possible but to allow continues drain @76AMP the pad need to be able to handle the heat dissipation of SMD mosfets. Which explain why they are overheated and blow. For same reason anything to cool this baby down will help bigtime!!