In article ,
David Lesher wrote:

(Drew Dalgleish) writes:

Kroil probably won't work if it has never seize on the threads but it
can't hurt to try. If it's really stuck it's probably faster to pull
the prop and ring gear than to mess things up trying to work around
it. Flying long enough to get the case fully warmed up may help too.

Not NeverSeize but pipedope, but I tend to agree. Another trick that
comes to mind is a large American Beauty soldering iron applied to
the plug, getting it hot enough to disrupt the pipe dope. (The iron
will not melt the case so that's no worry.)

You are better off heating the crankcase area with a heat gun and
turning the plug with the Allen wrench. Heating the plug will just
expand the plug into the case, whereas heating the case will expand the
aluminum away from the plug.