We sell Richard tons of core trans axles, LSD carriers, cams, spindles, LSD clutch plates, etc. etc. Back many years ago I told him how to stop burning up transaxles, by keeping track of/ checking the pinion shim stack. I will ask him next time I talk to him.
The gear teeth are hardened, including OS, and that is the issue, the welding after the fact, creates a very hard to relatively soft transition between the two parts and it fatigues. The only one out of the Colotti sets that has not broken is one done differently as far as how the old carrier was removed in that the original welded area was left alone and just the outer ring of teeth were cut off, thus the new weld was only between the two parts of a carrier, which is softer than the gear, avoiding the extreme range in hardness.
I have succesfully put needle bearings in stock alfa gears (1st, 2nd, 3rd)and Hybrid ratio sets, I run a set behind my 235 hp V-6 GT on the street and track.