The rig above that we did a substantial build on had a bad rear axle in it. The owner rolled his rig, bought another one and we moved all the good parts over to the newer one. What he failed to mention is after he rolled it, it was still drivable and after a few adult beverages that evening, he took it out and got into a tug of war with an F-150 in the sand and managed to blow up the rear axle. It came in on a tow truck and due to how terrible it looked, no way were we going to chance a test drive.
As I got more pointed in my questions about WTF was going on with the axle, he said he told us it was making noise when he drove it home from trailer storage. Yeah, but you said it was making a little noise, you didn't say it was blown up and you weren't sure you were going to make it home. You also didn't mention the drunken shenanigans.
Anyway, we took it to our gear guy, he replaced the gears, bearings, and all the seals. About a week later, the pinion seal went out, he replaced that, a week after that, both axle seals went out. Best we can figure is the housing didn't get all the broken bits flushed out and they eventually got picked up by the oil and circulated through the seals. What we do know is the axle was completely emptied, completely flushed, and we had no more blown seals after that.