I worked on an '03 for a friend awhile back, we added 8oz to new oil for 5k, then did 4oz in new oil for the next interval, is it cool to stop using the stuff entirely? He didn't seem to have any stiction, just 250k miles so we threw a lot of stuff at it at once. No noticeable difference, so to save $35 an oil change he wants to stop using it. No harm to just not using it anymore?