PB Blaster has worked for me a couple of times, I've also broken one trying to rush it...
If you can get it freed up, it would need the main screw, the pipe jaws, the horseshoe washer and an end cap to be complete... Might run up a bit of a tab on all of that, but the only necessities are the main screw ($$$) and the horseshoe washer.
I cut a piece of treaded rod just big enough to fit between the jaw towers, run nuts flush to both ends, slide it between the jaw towers and slowly back the nuts out, over many days, weeks...