Thanks to everyone who weighed in yesterday, it was all very useful.
The bottom line: Tristan's fine.
His back was pretty darn loose, only minorly locked up.
His biggest points of tension were in his neck, mostly on the left side.
He tolerated the adjustments exceptionally well.
Overall, the vet (who had seen him once, ten years ago, at a different barn, but understandably did not remember either of us) said "you have the healthiest senior mustang around."
That's good news!
I do feel somewhat conflicted, though.
Now the answer is, as always, "ride better."
It would have at least satisfied something if I'd spent a pretty good chunk of money (more than my monthly grocery budget; money I had set aside to buy new tall boots) and found and fixed a problem.
mostly he wanted a nap
I don't blame the vet for that, though. Getting the news that your horse is in terrific shape considering his age and his general health setbacks is reassuring, and for that if nothing else, I'm glad we did it.
Gotta work on that.