Please be aware of a few things. Penetrating fluids can take up to 24 hours to be effective. 5 minutes, 15 minutes, or even an hour, is not going to be effective. Heat, at least enough to be effective, can destroy temper and seals. I would avoid it.
A penetrating fluid applied and left for an extended time, combined with light strikes to the end of the head of the screws, should loosen them. This may take a while. Like days. Keep reapplying penetrating fluid, and use a punch and hammer to strike the end of the head of the screws.
[---T-- L -OlllllllO-]