How do you know it's not overfilled ? How many miles on this ? I use a ~50/50mix of Rotella syn 5w40 and Rotella T 15w50 on a 3000-4000 miles change schedule. I can tell you this some xt 660's seem to puke more oil than others, and some use more oil than others. They both run perfect....I can live with the variation, as long as they run perfect. if you are correct .2L in the airbox is excessive. Suggests that the crankcase pressure is high..