It's the gate valve for the hot water to shower, can only get a 1/2 turn. I wanted to unscrew faulty internals out of the vertically mounted one and swap for internals from identical good valve I have. Problem is, it won't budge. I thought of hitting it with a torch but I don't want to melt the solder. I was first going to try unscrewing the nut at the valve stem and spray penetrating oil and let it soak. What do you think. I'm obviously no plumber, but I do work on cars so I am somewhat mechanically inclined. Thanks in advanced