Screws frozen in plastic case

Should be a fairly simple fix on this, with the right knowledge that I don't have at this point.

I have a piece of audio equipment with a sturdy plastic housing, but 2 of the screws on the bottom seem frozen and will not turn
even after soaking for a while with WD40. The screws are not stripped and I have a screw driver that is the right size but somehow
these screws will not budge as if they have had glue included when they were originally tightened in.
Other screws around them came out, but with some difficulty.

Any suggestions on how to loosen things up and get them turning out for me ? Would PB blaster be too corrosive or damaging to drip inside
the case from soaking the screws in that ? Only thing I can think of at this point is progressively stronger penetrants.

thanks for any ideas