Originally Posted by d2jp
Have you tried PB Blaster or Kroil and keep soaking it with that for a few days? I haven't seen anything that stuff can't break loose with enough soaking and some tapping and/or CAREFUL application of heat.
Went through the same with my boat, even used Kroil and PB Blaster.......a little heat from a propane torch worked wonders!
Definitely would stay away from the chisels and such at this point.