The Kawasaki mule 3010 diesel is starting to leak pretty bad.. Since its previous oil change (2013), a fiber washer was used on the drain plug. It appeared to have stopped the leak until a month ago. I changed the oil and added a new washer hoping that was the issue and it is just as bad as before. Since last weekends use (as well as sitting/ dripping all week) it has lost about half a quart. May not seem like much, but it only holds about 3. In the meantime I am tempted to use some cheap 15w40 dino (Delvac, ST etc.) since it has to be replenished so often. Is there any high mileage oil additive that is worth a try? *If it was a gasser, I would just add some M1 HM 10w30 and go! Thanks.