The magic trick with any seized bolt (if wd40 etc don't do the job) - is......heat

If you don't have an oxy welder (and let's face it most of us don't) you could use one of the small butane/propane bottle hobby torches (they might sell em as soldering torches, i don't know)

That'd probably set you back less than $100 for a torch kit that has a hose and can be hooked to regular bbq lpg cylinders (which are astronomically cheaper to re-fill). The hobby torch like that won't be able to heat things to the point they are glowing red, so you are in zero danger of melting any metal bits. Just apply the heat for a good few minutes with some vice grips locked hard on the adjuster square bit, and after a few minutes, try gently rocking it back and forward about 1/16th of a turn in either direction. Usually you'll find that stuff that wouldn't even budge with Chuck Norris roundhous kicking the vice grips, will move _very_ easily once heated. If it doesn't come loose, remove the heat/flame, and re-apply some wd40, It will smoke a bit, don't go nuts, just get it lubricated, let it cool and then after a couple of hours, go back and reapply the heat for another 5 minutes and try again.

I've seen shafts that wouldn't come apart in a 10 ton press (mini outer cv rusted into a hub if anyone cares) come apart pretty smoothly after the application of heat (in that case an oxy torch, to be fair).

If you are having trouble locating any further bits (or if the adjuster just plain refuses to budge) - hold off on going on ebay, and post it here. I've a few spares (and I'm sure others here do too) that won't cost you the earth!

Keep us updated on your progress.