What I understood, and now stand corrected, is that they were having mechanical failure. The S-10's never came with a factory locking differential, but you can buy one in the aftermarket. I'll be willing to bet that is where GM is getting thiers from. They are probably some part desinged for aftermarket use, but GM got thier meat hooks on it and said give us an exclusive for OEM rights. ( I could be full of it myself right now, I dunno.) Anyway, since the S-10 have been around for a while and there are aftermarket lockers for them, I don't recall hearing that anyone has had hardware failure from that, so why should there be some in a factory installment.

Would an electrical problem such as not disengaging warrant a replacement though? You would think that the default mode if contact is lost would be for it to go to open. Infact, I believe it works on an electromagnate that once energizes attracts itself through a clutch pack or dog gear to engage. So loss of power would mean loss of magnetic field, and it would go back to open. If this is the case, would it be a lack of engagement solved by a simple cleaning/ replacement of the electrical connector? This doesn't seem to add up to a full replacement either. I dunno, maybe bad bearings in the ones with lockers. I'm stabbing in the dark for answers now, so I am back to putting on my bib waders for his bs.