Most 2-stroke engines get oil around the plugs. The rings don't keep the crankcase oil out of the combustion chamber, the oil is already in the air/fuel/oil mix so the combustion chamber is constantly bombarded with oil. The oil doesn't burn very well, so there is going to be oil around the plug. New plugs with new gaskets are usually better at keeping the oil inside the combustion chamber so it's blown out the exhaust. Try swapping in new plugs or gaskets and see if that helps.