I've been reading/lurking on this forum for over a year now and have gotten some great advice. Since moving to England, I've had to up my maintenance game due to the price of oil and services over here. It costs close to $75 for an oil change. I own a 2000 Toyota Avensis 1.8L 7AFE lean burn engine with 133K miles on it. I bought it from a local rental company and there was no telling how much abuse this thing had before me. Over the past year I've had to replace the battery, water pump, timing belt, air filter box plus filter, spark plugs, spark plug wires, moon roof controls, and flushed the radiator/transmission. I did my due diligence and researched the only high milage and synthetic oils offered by the base exchange. I decided to clean out the engine with M1 10w30 and Castrol 5w30/10w30 HM. I shortened the OCI to 1,500 miles and started to alternate between the two oils to clean and swell the old gaskets. Now that I've been doing this for a year, should I change the OCI to 3K or 5K miles or keep them where they are? Also, if my engine is running smooth with the Castrol HM should I even bother with the M1? M1 is $2 more the the Castrol and it adds up to $8 more per oil change...not that I'm counting.