I've been a proud owner of O.S. Engines since 1996. I have two identical 61 FX Engines, one is only a year old. Both O-Rings on the Needle Holdern failed at that the beginning of the flight season. I have been wondering if something in the fuel could be causing these O-Rings to go bad. I have always used OMEGA 10% or 15% nitro by Morgan Fuels, and I have never had an O.S. O-Ring go bad before. (I used to fly with 15% Nitro, and Now I fly with 10%) The O.S. Manual says do not inject after-run oil into the carburetor. I have faithfully followed steps stated in the O.S. manual.
Link to Morgan Fuel:
* The O-Rings became brittle and broke.