WD-40 isn't a penetrating oil, the stuff sucks accept at removing moisture. Get you some of that, any brand will do. We can't even buy the best penetrating oil know to man hands down, period, but we can make it!!
50/50 ATF "Automatic tranny fluid" and Acetone.
Could be somebody Loctited the screws and ferrels in place because even if the screws won't turn the ferrel should back out. If it wasn't the Blue you're in a world of hurt. Screws can be drilled and replacements are cheap. I'd want to see under those grips given the condition of the rest of the piece.