Jules wrote:
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?

Have you tried tightening it? Sometimes things will break loose when turned the
other way.

Have you tried the hammer and screwdriver at an angle trick on the nut to try to
turn it with impact?

Have you tried a pipe on each end of the bar to double the force before the bar
bands?