After-run oil is a marvelous thing for our little Motors. My opinion is if you're flying at least once or twice a week, your engine doesn't really have the chance for time and corrosion to take it's toll. However, there's nothing that says your gonna hurt anything by doing a little preventative maintainence. The main thing here is to displace moisture. I like using PB Blaster. Anything that's gonna work it's way into your bearings. It's especially useful to use the after-run in engines with bushings instead of bearings. Since they're more metal on metal, that first few seconds when they're started up is hell on that crankshaft.