This seems like it was overheated or running under lack of lube, did they fill this diff up to level when originally installed, It doesnt look like shock load it looks more like overheating or lack of lube more than anything you can see the axles almost changed colors, very strange the only was this would happen is if there wasnt enough oil. I've seen alot of 2.64 diffs go because of shock loads on a step incline specially when coming out of underground dock. drivers get on the gas a little to hard thinking their truck will roll backwards i've changed plenty of those, but if it was a shock load, it would have twisted the driveline as well maybe not so you can tell with you eye but once you put it on the road that truck will be shaking like all hell is breaking loose.
Valley is who Mack and Volvo use. The ONLY reason I had Valley was because the first time I didn't know any better and agreed to get Valley, but last year I couldn't get anything else because of Covid. VALLEY remains are junk. I've had 4, yup 4 fail in less than 300,000 miles and they were all covered by warranty. OBTW I PAID extra to get a no questions asked replacement 3 yr unlimited mileage warranty Two were the front drive two were the back drive. Nothing to do with my driving they are just JUNK. I have made a rule no more remans from ANY one. Brand new is the way to go.