Leather corals do what we call sloughing. They will be OK for weeks and then all of a sudden look bad. They will even shed a layer of skin for a day or two and then they will be Ok for another couple of weeks and the cycle goes on. I have a finger leather I have had for 15 yrs now So I do have some experience with them. I have fragged mine several times over the years but still have the original.
You can view many of my fish and corals in my photo albums in my profile.