We and our glow engine manufacturers recommend the use of after-run oil in all engines because we've just seen too many cases of corrosion. After over-lean running, corrosion is the most common cause of damage to model engines. We don't know what fuels are being used, we just go by what we see when they come into the shop. You cannot damage your engine with a good shot of a good-quality oil into your engine after the day's flying. Run it dry of fuel and then load it up! I have an engine that was loaded with oil after the last flight and then it sat for about 15 years. Still turns over smoothly.