I have a new ZDZ40 and after running, there is an oily mess on the cooling fins. There is clearly a leak. It is escaping around the outside of the ring that surrounds the spark plug, not inside the ring where the plug is. The oil does not come out all around, but just in one spot. I have the plug torqued to 15 foot pounds. It did not come with a washer, just the plug and that ring. Any ideas what to do?