Well, the part arrived in the mail yesterday and before sundown, I managed to remove the circuit board from the generator box; used a solder sucker to remove the varistor, which crumbled in to three chunks; soldered the replacement, but decided to wait till morning for reassembly.

Switched it back on this morning and the fix worked. Now I have to reset the generator monitoring values, but have to do tests to confirm the values (salinity, temp, amperage) and the chlorine output.

Then I noticed the that the top of the DE filter valve was weeping, likely an O-ring . . .