We have one of those jacuzzi tubs in our bathroom and we'd like to use it. When we bought the house, the inspector didn't catch the fact that the hot water valve is locked in place (cold water one works well). I took it apart and everything looks fine to me (pics below). I had a plumber come for other reasons and had him look at the valve, and he said that he doesn't know if it's "seized up or just stuck", and that if it's seized up and breaks somehow, he would have to break the tile to get to it, so it's probably not worth doing anything. It's all Kohler but I don't know the exact model.
Is there anything I can try to do to fix it without risking damage?