Joseph,
I'm almost definitely overthinking this... but once I get it into my head it's hard to unravel my plan. My hope is that at worst I'm just paying too much for a product. WATER PUMP!!? I'll have to tear it out ;)
I'll let you know what I find out. In the meantime I've got my heater box off & disassembled. Will clean /refinish it, replace core, and get it back on in a few weeks.