Anyway, I gave him a year off, hadn't seen the stumbling and started riding again. After a few weeks of light work he made it clear he didn't want to be ridden. This time I had out the chiropractor and then a different vet for another work up. He didn't present as lame, but the vet did say he's neurological on his right hind, and possibly his left.
The vet said I could do quite a bit of diagnostic work to see where it was coming from, but that he didn't see it as EPM or degenerative, or he thinks we'd have seen it get worse. We think the pain comes in when Miaren compensates for the control and uses muscles and moves in ways that then make him sore. I've heard of a number of people spending quite a bit of money to find the source, but very few who said that it was useful in bringing the horse back. He seems mostly normal on pasture, I can tell he's moving differently than in the past, but nothing someone who didn't know him would notice.
I will probably put him on a supplement that my trainer recommends, but it seems the kindest thing is to retire him. Over the summer he seemed fine when I first started working him, so I'm thinking that flexing and turning aggravates whatever he does to compensate. The vet really had to work hard to find any signs, but I know when he's stumbling behind and the vet could catch him not using the right hind correctly in his tests.
So, after the next farrier visit I'll pull his shoes and send him to live out with Emma, the Shire. He's not a lot of trouble at my place, but he's not made friends with the other two and terrorizes them a bit. I'm hoping he'll buddy back up with Emma and maybe he can have a grooming partner. Right now I'm it, and I don't scratch for nearly as long as he'd like. He's coming 14, so this is hard, but maybe I can take him out to the kennels some times to watch the hounds working from the pasture.

He loved jumping.

Out with the hunt.