You might find that an "exhaust deflector" is a good investment:

http://www2.towerhobbies.com/cgi-bin...&I=LXL378&P=ML

You simply attach the rubber tube with the supplied zip ties to the end of your muffler. This allows you to point the exhaust down and away from your wing a bit, and it will reduce the amount of oil stuck to your Nexstar. They have a habit of falling off in flight if you don't get the zip ties real tight, but at $3 each, replacing them isn't a huge hassle.