Byron,
I am somewhat baffled that, as a licensed EC, you don't seem to feel a bit of urgency in the fact that you're describing a metal box and fitting GLOWING RED HOT!! It's simple to figure out that you've lost a neutral somewhere downstream (It's not the poco's issue if they already checked their side under load,) and current is finding a HIGH impedance path back to the main service. I certainly hope no one bumps their arm on that service and gets nailed [Linked Image] !!

SHUT THE POWER OFF!!! If you can't find an obvious place where the neutral/ground are being tied together, other than at the main service point, then
turn all the branch breakers off, disconnect your neutral feeders to the subpanels at the main service disconnect and ring them out to ground. (Open noodle test) You shouldn't get anything. Likely from your described scenario, at least one will give a reading.. Follow it until you find the point downstream where it has faulted and/or been tied together with your grounding. (a toner might be helpful here incase the wire itself might have failed underground)Follow it from point "A" to point "B". If youre lugs were tight and not corroded at each end, you'll find it along the way with the toner when you lose tone.

I might also suggest replacing the parts that became "burning hot", and even though it may not be required, pull a properly sized ground wire to help eliminate "glowing fittings" should another fault occur down the road. You stated you found loose fittings here and there... It's an easy "peace of mind".

Of course, this is all dependant on your jobsite not becoming a "Structure Fully Involved" call to your local fire department before you decide to lock the power out!! [Linked Image]