To illustrate the whole point about additives, consider this. In the manufacture of synthetic oils, once the synthetic polyol ester bases are created, anti-wear additives such as zinc dithiophosphates (essentially combinations of zinc, phosphorous, and sulphour molecules) are added. These combinations are extremely effective as anti-oxidant, anti-wear, anti-corrosion inhibitors. Now look at the contents of some of the after-market additives. Wow! Zinc, phosphorous and sulphour! Imagine that. Those aftermarket additives are actually exactly what your oil manufacturer has put in already. Consider further that some oil companies actually make a point of telling you not to use aftermarket additives with their oils. So if these additives are so brilliant, why do the companies always seem to end up in trouble? Well - misleading advertising and non-active "active" ingredients claim a lot of victims.