Back from the vet:
She thinks that Red has a mild case of locking stifle on his right hind. It doesn't ever lock fully, but it catches every now and then. She had me hold my own hand over his right stifle and I could feel it when it did it at the walk. We did x-rays just to be sure nothing was going on arthritis-wise, and the x-rays look great.
So I'm relieved that it isn't anything serious, and hopefully will be something he "grows out" of. I'm going to try to do lots of hill riding until the snow/ice appears for winter, and then pick it back up as soon as footing is safe in the spring. She said there's the possibility we might have to do surgery in the spring to scar it together, but at this point, she highly doubts we will have to do that because it is not that bad of locking stifle.
It makes sense that it is his right hind that is bothering him, because he turns a barrel worse to the right, where he should be bringing that right hind underneath himself (but he can't).
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.