Here is another picture. Any cleaning better that this would probably require some kind of solvent, which would likely damage the good insulation nearby as well. I am planning to coat this area with corona dope before I apply power in any case.
Tom, the original wax is not feasible to re-use, as far as I could imagine doing. My concern with trying wax again is that if anything happens in the future such as a short at the same spot, another wax meltdown would likely destroy the part and maybe much worse. You have a good point about wax being more easily re-done/reversed, though.
Old Coot, without the HV rectifier, am I still looking for/expecting the full high voltage to develop in the flyback coil, at least if I get the variac anywhere near 110+ volts? If I am, then I would need to plan for and insulate against new arcing, I would expect, since the entire coil is now uncoated.