One of the Dana 60s that I built recently had to have the inside of the case machined where the carrier bearing cup fit in the housing because it had spun under stress. That seems to be a common issue in high mileage and heavy duty use. My answer to that is to be very careful in the pre-load setup and to use synthetic gear oil with a large capacity cover for more gear oil. I wish I was building a S60 with the adjustable carrier bearings, but I build what I have.