I have a Shin Deshojo growing in a pot on my deck that I purchased from Greer's about 5 year ago. It appears very healthy, even to the point where I've pruned off some of the growth to keep it within bounds and thickin up the branch growth. The leaf color this spring was spectacular! Anyway, here is my question. I've noticed a sticky, almost sap like substance, appearing on the surface of some of the leaves. It washes away in a rain but comes back fairly soon after (7-10 days). Is this something that I should be concerned about? The picture is my attempt to show what I'm talking about.