I have one of those heater element sockets which have holes in the
end to take a 3/8" shaft - and I had no problems with the upper element,
but the lower one is jammed up solid; with some 3/8" metal rod through the
socket holes and a 4' thick-walled hollow bar on that as a breaker, it
just keeps on bending the 3/8" rod where it meets the socket...

Heating around the element nut with a torch hasn't helped, nor has leaving
the whole lot to soak in penetrating oil for a few hours, nor has
thumping it with a big hammer to loosen the corrosion (makes me nervous,
that, though - tank looks to be cast iron, and I don't want to crack it).

Worst-case I might be about to drill the darn thing out, I suppose,
although I was mainly interested in checking the element for scaling, not
outright replacing it (it's giving 13.8 ohms consistent with the upper
one, and nothing to ground on either terminal), plus i don't want to risk
trashing the tank threads.

Next attempt might be to drill the holes larger in the socket, as I have a
bit of 5/8" solid rod sitting up in the workshop - but before I go
modifying the tool, I was wondering if anyone had any other bright ideas?
Maybe leaving it to soak overnight in penetrating oil is worth a shot?

cheers

Jules