Free: Contests & Raffles.
What did you put on the screw for a release agent?
As already mentioned, use the correct screwdriver. I follow Mark Novac's Anvil gun restoring videos, he uses a 2 oz and a 4oz ballpein hammers to loosen screws.
They actually make a tool that turns to the left when struck specifically for this type of situation. I have used them for removing screws on airplanes but can't for the life of me remember what it's called.