ST506/412 failure modes? (in this case, an IBM 0665)

Afternoon all, This may be forgotten knowledge - or perhaps more likely, something that was never known in the first place - but are there any typical failure modes of ST506/412-type drives (beyond the obvious mechanical damage between heads and platters)? I've seen quite a few dead drives over the years, but of course haven't invested much time into thinking about what might actually be wrong with them, because they were once quite common. Now that working ones are getting scarce, it got me wondering if there were any obvious things to check. In this particular instance, I've got an IBM 0665 30MB drive in a Compaq which spins up, bounces the heads around a little, then causes the machine to issue a fixed disk failure at boot time. This is an embedded servo drive with a voice coil, not a stepper type. Oddly enough, it passes Compaq diag's spare cylinder read/write tests, but fails the seek test. I've not tried a LLF yet because I was interested in trying to salvage whatever data might be on it first; there are several large ASICs in the logic board, but also a lot of more common stuff, so it's possible that the fault is something fixable - but checking component by component is probably more trouble than it's worth. Yeah yeah, MFM emulators and whatnot... but I do want to keep noisy old boat anchors alive in my machines for as long as I can - while a modern replacement is the only long-term solution, I always think of modern tech as detracting from the experience of using old hardware. cheers Jules