Fuji,
I don't know anything about aero engine rebuild spec or aero oil specs,do they clear out all the oilways etc during a rebuild and whether Elite is high detergent?
I was just specultating on possible causes from a competition car / race engine point of view.
We tend to use 100% synthetic oils in race engines as they definitely give better high temp protection and keep the engine very clean,although I don't think synthetics are used so much for 4 stroke aero engines but stand to be corrected.
Lister