I want to replace the shower valve for the cold water side of my shower; it leaks and the knob turns all the way around. It doesn't shut the water off and I think it needs a new washer or valve. After watching several YouTube videos, I thought I'd be able to complete the job over the weekend. But after spraying the valve with WD-40, Liquid Wrench (this mess caused an allergic reaction/irritation), using shower socket wrenches, the valve will not come out. I can't turn it (I've tried turning it counter clockwise) and do not want to break the pipes. I saw a YouTube video where someone sawed off the valve stem, used a spark plug thing and a socket wrench to get their valve out but I don't want to do that because what if it's still stuck?

I think the valve is corroded--the bolt/threading around it looks old and worn. My home was built in the 60s and it's probably the original valve. I have no idea what brand it is. Any advice on how to get it out without tearing up the wall or cutting stems? Thanks in advance.