A fellow Bolter and local buddy (same guy) told me of a way to get stuck bolts out, I'm sure it will work with screws as well, the trick is to do this BEFORE you bust or otherwise make the head of the fastener un-usable or broken.
I went to a local hardware store and got some Bee's Wax, heated the stuck fastener using a torch and applied the bee's wax to the head of the fastener. The Bee's Wax wicked into the joint and the fastener was freed up pronto! I used this on the door hinge bold on my 57 GMC 100 panel, works like a charm!
Thanks Greg!
PS: WD-40 didn't do a thing.

1999 GMC Yukon
1957 GMC 100 Panel