I have a fairly new Egg (bought this spring). It has seen extensive use. I have noticed a few "gritty" bites in some of the things that I have cooked. Is this just dust from lump that has blown up onto the food? I have also noticed pit marks on the grill surface. I have done a lot of high heat searing and am wondering if all of this high heat is wearing the grill out. Could the gritty bites be bits of rust or metal that has releades from the grill? How long would you expect the grill to last?