Thanks for the observations, as I may have made a false connection between the coincidental ocurances of oil level and gas grade. The oil level has not changed since topping it up, and given the sudden onset of hot muggy weather in eastern ontario, then perhaps the engine is now having to deal with this environmental change which has an effect on oil.

If low octane gas is more quickly used than high octane (then by inference "cleaner"), would it be better to fill with low octane and use octane boosting products to get "premium" cleaner gas?