I would maybe recommend getting his head xrayed to make sure there is no tooth root infection or hairline fracture which may not be obvious from examining inside the mouth. There is always the possibility of a foreign body embedded in the soft tissue which may not be apparent - a friend of mine...
I have to say I'm one of the people who swears by Pernamax. Having tried Cortaflex, Synequin, Cosequin, Aviform Supplease Gold, etc, etc, with no noticeable effects, within 2 weeks of using Pernamax, my big warmblood with DJD in his hocks was a different horse - he's been on it for 6 months now...
I have a huge warmblood with a massive front end and not much behind. He has high withers and enormous shoulders and whatever saddle I put on him seems to sit uphill at the front and too low at the back. I need to buy a used dressage saddle for him and I'm wondering what type I should look out...