[speeder]

It is extremely desirable to have a clean engine with all oil and coolant passages clear and no sludge on rings, etc. The argument is whether it is smart to try to "flush" the gunk out or just keep it clean in the first place with regular oil changes. You also cannot discount the importance of using the best filter available.

Off-brand or store brand oil, (like the STP brand in Autozone), can be 100% as good as Mobil1 or other name brand oils. You need to learn how to read the back of an oil container, where the additives and certifications are. Filters are another story, however. There can be a huge difference in filtering between brands. There are studies done that are published online showing the ineffectiveness of K&N filters, for instance. I always only use dealer filters or known OEM brands for my old Mercedes cars, like Mann and Hengst.