I had never used after run for the 2 1/2 years I've been flying. It was just a pain in the kiester, messy, and seemed like a good way to introduce contaminents into the engine. Then, I had to send my Saito 100 in for service 2 months ago. I got it back 2 days before Christmas, along with the old bearings. They were rusted to a point they were pitted. I couldn't believe my eyes. I add 2 oz of castor to every gallon I burn, live in a virtual desert, and then this? Rust? ***? Now, I reluctantly use it in my four strokes. What a pain in the *****.