What are your thoughts about engine oil additives, such as Slick 50? I'm talking about the things which are supposed to reduce friction and reduce wear in the engine, possibly improving fuel economy. There's a bunch of these on the market, but slick 50 comes to mind first. I suspect their claims are wildly inflated, and that frequent oil changes is the best thing you can do. I will admit that this is unsubstantiated speculation, though.