Do you ever actually change the Mobil 1 (pull the drain plug), or do you just go on and on by changing the filter and topping off? If oil is good enough, and the filters are good enough, that should work. I'd like to know of several people who've done that for some time before I try it. Oil, even Mobil 1, is cheap to change every 6000 miles, compared to the cost of an engine. But I'm always willing to listen to an idea that might work.