I have a 1981 HP V4 Evinrude Model #E90MLCIM. There is oil leaking out of the exhaust cover. It runs great but the plugs are a little wet when I pull them after a day on the water. If I mix the fuel (normally 50:1) a little lean it does not do it as much and it also gets better mileage. I don't want to keep doing this in fear that it will lean out and damage a piston but don't know why the excess oil??