It actually looks like just the one hind pastern that is weak. Perhaps if you can get some better shots with him standing relatively square with all four feet on the ground, we can better tell. But I'm looking at the one with you standing him in the arena, and it's just the left hind that is weak.
Other than that rear leg, he is a really good looking horse from what I can tell. I like the more 'uphill build' in a horse...usually will make collection a bit easier, as they're 'inclined' to the rear...or would that be declined? Hahaha. At any rate, he's a nicely built horse atleast from those pics.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."