I always used to use 5/30 in mine & the consumption was absolutely nil. Flushing, as Mistermena states, causes the carbon seal formed on piston & rings to be dissolved. It will gradually reform especially if you are now using a little bit of oil. I personally always used to use semi-synthetic 5/30 & changed at approx 5000mls. You can use 10w/40 as this is a little heavier but will take marginally longer to circulate around the engine, especially in the now cold weather. A 5w/40 could be used, giving cold weather starting protection, but is often only available as a fully synthetic oil & therefore a bit more expensive. Also, why use the more expensive petrol? Normal unleaded is fine. It is not a high compression performance engine & providing no pinking occurs, will be entirely suitable providing the timing is correct. If you are wondering why I'm talking in the past tense, it is because someone decided to alter the shape of the rear of the car by driving forwards but looking where they had been! Happy motoring!