The person I dealt with the time before last told me he'd dealt with similar problems in the past, and that they could be remarkably intractable. "Haunted," was how he described the afflicted systems, which seems apt and is the best answer I've gotten so far. Still, I wish I knew what the hell is the matter with this MacBook. Academic or not, it bugs me.
(Because replacing the motherboard fixes it, right? It's just that it comes back without fail inside of two months, and then gets worse as time goes on. I don't buy that I had four defective motherboards in a row, so there must be some other part—which they haven't thought to replace—that's malfunctioning in such a way as to put undue strain and wear on the motherboard. Like, using a slightly wrong voltage or occasionally sending power spikes or a short? Does this sort of thing just not occur to the repair division, or is it just more cost-effective to replace a system than to exorcise this caliber of issue?
All I know at this point is that I'm damn glad I had the 3-year coverage.)