The owners manual specifically states to NOT go over the max point, and it could cause damage. Check the manual as I forge the actual page it is on. It may not have done any noticeable damage right away, but over time, it may have gunked up something that will slowly cause issues later. Better to have it checked/repaired while still under warranty that after warranty is up. Ever since a Subaru dealer overfilled my Subie 9 years, ago, after every oil change, I always double check it... before I drive more than 5 miles. Better safe than sorry...