Luckily I had already bought a new saddle (Wintec Pro with Cair) and he approved of that one, so we'll both be more comfortable from now on.
He gave him a chiropractic treatment, which Starship thoroughly enjoyed and hopefully fixed the spots that were leftover after 2 weeks rest. I was allowed a light ride today and could already tell the difference. He gave with very little pressure, that is not normal.
Bad news on his knee though, much worse then I thought it was. He has lost 50% of his range of motion and the arthritis is making it very stiff. Weather is not helping right now of course, but I guess living in Arizona we're very fortunate.
He is ok to ride often, however I'm to avoid small circles to the left. So much for serious dressage, but he's already had a successful racing career, so I should feel fortunate that is the only restriction we were given.