Following a few more occurrences like this incident and a bit of debugging and analysis, I finally decided to bite the bullet and replace my motherboard. Because the processor is semi-old (an Intel P4 with Socket 478) I wound up replacing it too rather than trying to choose one of the (very small selection of) motherboards that supports it. Eight hours after placing the order with NCIX it’s been shipped, and for $50 less than anywhere else I found; both prices dropped by a substantial amount as I was browsing. That’s a pretty good deal and speedy turnaround, both of which I’ve come to expect from the company.
So with any luck grok will be not only stable but better, stronger, and faster than it was before, sometime this weekend.