Got a propane torch?
Heat up around the plug and give 'er!
Can't say I've ever seen one seized in the cover before...

 

Get some PB blaster (better than wd-40) and apply it a couple times...... Lightly, yes Lightlytap the plug with a hammer. If that dont work heat it up with a torch as previously mentioned. When you reinstall the plug put a small amount of anti seize on the treads.

 

what would i do without the forum?