No surprise MSI is unwilling to let go a schematic, I guess. I'm sure such documentation would fall under MSI "trade secrets" -- can't let any proprietary info out lest they risk losing their competitive advantage.
Service manuals, however, can be written to hide sensitive information. There's even a connector (JLPC1) which I suspect is used to help diagnose hardware problems. *Any* info that MSI would be willing to offer to help me debug this would be useful!
The POST failure is a recent development. It began intermittently, and became more frequent over time, until finally it wouldn't start at all. But every time the BIOS managed to initialize, the board ran beautifully in every case. I've ruled out all but the K8N Diamond Plus itself (via swaps with redundant components on other operating boards), and the fact it runs great once initialized tells me the problem is related to the BIOS. This problem "feels" like a pull-down, trigger or broken trace someplace. And I've already used contact cleaner to hopefully ferret out any dust bunnies causing shorts.
I've asked MSI whether they would still service this board out of warrantee. So far no response. In the interim, if someone with MB hardware development experience can even throw out a common/probable failure for these boards that causes what I'd described (4 red LEDs), that would be a good start.
I appreciate the offer for parts. If I manage to identify which one is the problem (w/o a schematic *sigh*), I'll definitely take you up on it!