would it be reasonable to deduce that the battery is in a perpetual under-charged state (ie: it's dying)?

I saw the battery terminals last week, it came back pretty dang fast.

I did the grease trick. Just use lithium-based auto grease, so not technically electrical rated. It worked. Downside is I believe THAT is when the acid found an air gap and went UP the wire. It's much easier to clean when it's localized around the terminal than it is to diagnose a rotting cable under the insulation.

Good luck, but right now my $$ is on the battery.

When way to know for certain that would cost $100 instead of potentially damaging ANOTHER $300+ high end battery: Go to walmart and pick out a basic lead acid battery. Run it for a few months and see what happens. Should be $80-100.

If the corrosion returns: Alternator is jacked up. If it doesn't, battery was dead. If the alternator was shot, replace it and put the Optima back in.