Hello,  I never had any luck with Liquid Wrench on pot metal but there
is a penetrating oil that might work.  I have used it on Play-a-Saxes
that did not come apart with reasonable twisting and pulling.  It is
called Kroil and should be found on the Web.  The company tries to sell
you a 55-gallon drum with the offer for a free hat or something and it
all looks somewhat fishy but the stuff really works.

After two days soaking a really tight Play-a-Sax pulled right apart.
The stuff is called Aero Kroil and it seems that Amazon has it.

Best regards,
Spencer Chase