Originally Posted by JoeD
If there is no short to ground just plug the damn thing in and try it. You are over thinking this.
If it heats
and does not have the case energized with 120V with respect to ground
and this 120v if it exists is a phantom voltage
and the heater does not trip a breaker
it almost certainly is OK.
I would have measured the element resistance and checked for many, many, megohms from the element to the case, then plugged it in and checked the case for not being energized.
That's Due Diligence and a Duty of Care in my book.