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

Acetone and trans fluid has been tossed out there for years.

I had one that was frozen up pretty good, I soaked it in PB Blaster for weeks, sprained it every day.

It would not rotate.

I ended up protecting the shaft ends and started tapping the shaft to the left then the right (just a little) over the next week I got it freeded up enough to rotate.

A couple weeks later I found the manifold had a crack (not from anything I did) so I ended up tossing it.

But I got it completely freedup.