Heat is your friend- - - -Use a Propane or Acetyline torch, get the plug hot (almost red), and apply a block of paraffin or a candle to the threads. The wax and heat method works much better than penetrating oil to free up a stuck thread.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!