So how is Marvel different from Seafoam? I seem to remember a recommendation from someone (or maybe it's even on the Seamfoam package) to only add the detergent in the last X many miles before an oil change. Agree that you're cleaning the gunk if you put it in at the oil change, but where is that gunk going over the 3-5K miles between changes? Is it just clogging your oil filter that much faster?