This might sound crazy but could the cases be tweaked and fatigued from failures and hours of running?

Thaysbwhatbi am thinking, or just a set of gears let go that just happens too I guess

What gear oil do you run in them?

I have ran valvoline 80w90 for years.

for me it was the lowers vertical shaft,,I'd snap those things like nothing and in turn would window the lower case.

how are the lower gears dying?Can you post a pic.almost sounds like a set up problem but then after that,something could be moving in the case to lose the back lash and bearing preload.

Arneson and never look back.

Didn't take it apart yet but it's not setup, my buddy knows these drives been doing them for years never had issues, really thinking its a case issue but could just be bad luck too

text me a pic of the last set of gears..i would like to see the contact pattern..

by feeling it there will not be one like the last set that totally exploded.....