I inherited my grandfather's old woodstock fireview a few years back, I think it was made in 1982. I only use it on occasion when I am working in my basement. The stove has a crack in the stone on the very top of the lift up top. The crack does not affect the operation of the stove but I took a trip up to the factory and they helped me find a matching replacement stone. The trouble is I cannot get the 4 large regular head screws out of the cast iron frame that holds in the stone on the back of the lift off top. I think that I have tried everything including liquid wrench, LPS, heat. The screws are not rusty or damaged, and they look like they should back right out. Any suggestions?