Both DTI's Cosslett and Dynatrac's McGean report that they see very few shock-related failures (such as heavy application of 'wheeling torque) to either 60 or 14-bolt diff internals. Due to the shim setup used to set the ring-and-pinion in 60s, older 60s tend to wear the thrust surface in the case. If the wear gets bad enough, it can cause excessive ring-and-pinion play, leading to more problems or failure. Sometimes 60 cases must be remachined to repair the thrust surface. This is only a concern when looking at high-mileage, used axles. The same sort of thrust wear occurs in the 14-bolt, but it wears against the lock ring, which can be adjusted to compensate.