I cant' think that if the gears look good, that the diff got too hot.
I have personally seen a diff that came out of Tracey's 510 after a 7 hour Enduro we did at Westwood. There was NO oil left and the gears were BLUE and BLACK..baked! It is amazing that it ran the full length of that race.
This is when Andy realized that with shorter gears and sustained high speed driving, that the requirement for a larger diff cover was a pure bonus for longevity. That's why I would love to have one of Matt's billet covers. I change my diff oil regularly as our 400+ mile drives, with 4.6 gears doing a zillion rotations, all translates to heat. Our only saving grace is that we are not caning on it the whole time, so the loading is even greater.
I would say that if some were loose, and one was over tightened, that the vibration cycle maybe just finished it off?
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer