Unfourtunatly, all that goo coming out of your exhaust is exactly what should be there. That left over oil is what was cooling and lubricating your engine. If you lean to the point the goo isn't there, neither is the cooling or lubricating your engine needs. You can loosen the bolt that holds your muffler halves together, and turn the small outlet spout to a better angle to try and keep some of the mess off your plane, as well as using an exhaust deflactor. Or do as the rest of us have, invest in paper towels and a cleaner to wipe off your plane at the end of the day. I personally use dollar store window cleaner with about 1/4 of the bottle dumped and replaced with alcohol. (but that's a diffrent post all together)