There is actually no known therapy or treatment for a horse that doesn't sweat. Juuuust an FYI.
Also... in regards to a horse that is hanging a leg. You could always try to break up the monotony by making smaller jumps just a bit more of a question. Scary things under them, corner fences, skinny, not just your same old average vertical and oxer type of stuff. My horse can do the meter fifties. But do you think I go charging up to a meter fifty fence every time we school? No.
So he needs to remain competitive at the 90's and the meters as well. Grid work, and keeping it interesting for him is what works for me.