I used 5% WildCat or PowerMaster DF fuel. I've had O rings last 10 - 15 flights. And then put a new one in and only get 4 - 5 flights. I had the best luck with the white ones that JMP used to sell. They are getting hard to find. Also, all of my .77s and .91s had the JMP machined exhaust header on them. I think that helped O ring life. We used to replace glow plugs every 4 flights, whether it needed it or not. The last several years I have just been running them till they die and some lasted 20 or more flights.