The original battery backup was not a viable option. The battery holder was completely corroded.
Bob Roberts has a page detailing the removal of the old holder and replacing it with a 2032 coin cell battery and holder.
I found a dead motherboard with the holder and removed it. Soldered it into place as described, and added the jumper wire. Fired it up, changed a couple settings…viola! It saves settings again.
I’ll keep an eye on it, of course…I’ve heard of some boards that will drain the battery quickly because of something in the circuit that isn’t right. But I’ve got full confidence that this will not be the case.