What's the best solvent for freeing up manifold heat control valves?

No, it's Sea Foam in a spray can. I would spray heck out of it, let it sit and then gently tap on each END of the shaft tapping it back and forth. It won't have a lot of room to do that, but it will move enough to help get the sea foam in around the bushings and the shaft.
Sounds good - thanks.