Thanks for the treatise Jim, good stuff....
I always check the coolant with a volt meter, and have seen as much as
6 volts from the coolant to ground.
If a flush and fresh coolant wont eliminate the voltage, I'll add a
ground strap from the radiator to the body and engine.
In stubborn cases, and with plastic radiators, I'll add 'Napakool', a
coolant additive until the volt meter tells me to stop.
Just my unrequested 2 cents worth....