Beautiful plant. I also enjoy this cross but for some reason I keep having one leaf rot then another. Before you know it the plant is much smaller then it was. Maybe it's just mine that do this.
Bob, I don't know what might be the problem causing the leaves to rot; but, it seems that a repotting into fresh mix is in order. It could just be sour mix and a whacky pH. Fresh mix should solve the problem. You'd be better off to do the repotting before the plant goes downhill too much. Otherwise, it'll have the repotting stress to deal with on top of being weak from losing too many leaves. Good luck.
John the plant is growing in S/H so repotting is not the issue. It happens to both of my plants of that cross. My only guess would be that I water with very cold well water. That water comes into the greenhouse before it goes into the water softener. So if I ran a hot water line in there, that water would have salt in it. Oh well, one can't grow all paphs.