I posted this last week in the Cacti and Succulent forum, but I probably should have posted it here. Also, I'm including a couple of photos. Don't mind the long-tailed mealy on one of the leaves. That's a whole separate issue. So far, we think the problem is either oedema or mites. We can't see the mites under a magnifying glass and someone suggested that they may actually be living inside the fleshy leaves. Is that possible? Any suggestions would be very helpful!
Looks more like oedema to me... If you have burrowing mites there should be a visible entry hole somewhere on the leaf...