.....so if high mileage engine oil is supposed to have extra additives to extend engine life, would a motor with less than 20K also benefit from its use? I understand that it also has some ingredients that are suppose to help reduce sludge, is that it's real purpose? Wouldn't an engine with routine engine oil changes at regular recommended mileage have reduced engine sludge anyway provided you are using something besides low grade oil? And is there really much difference in one brand to the next? TIA......next I'll ask about synthetics ? : )