Look at my broken gears!

[RC-Monster Mike]

The problem is usually wear. Whe the diffs are first built and shimmed, they are almost bulletproof, but the parts wear, and when the shafts get some play, in conjunction with serious power, they fail. I have never blown a fresh diff inside aluminum cups and cases, but the ones I have had fail are always worn(I notice the wear, but get too lazy to rebuild/re-shim them and they eventually fail).
Dual brushless 14+ pound trucks can eat a diff up pretty quick! 1/8 diffs is really the best solution for this beast, John.