There are RV-12 owners, including one flight school that I am aware of, that run Mobil 1 4T RACING Motorcycle 10w-40 full synthetic motor oil, due to it's gearbox additive, which suits the purpose of a motorcycle motor oil that shares engine and gearbox duties.
If you do decide to run this full synthetic motor oil, understand that you can run very little 100LL in the engine while on this motor oil. It requires almost exclusively Premium UNLEADED Mogas. Full synthetic motor oil does not suspend lead well in the motor oil.