rutan - I was taught that lead also assisted in heat removal by the unburnt fuel air mixture out of the cylinder.
It appears that for some reason the exhaust valve and its guide area are now getting and remaining hotter than they use to, given that it is not just Lyco' but also PMA cylinders and even TCM's. I can only conclude that it is pilot error in operation of engines. ( I have my AWI interview next week).