Choose a good oil of your choice. Nothing would be harmed with that mileage. I'm beating myself because I know what is in mine and not sure I want to go that way. Mine now has 30k and I'll have to make up my mind soon. I am a big Dino 20/50 Castrol fan. but this thing is a Synthetic baby. I don't think in the end it makes much difference which way you go. Pick a good oil and change it as it should be. I'm leaning towards synthetic for this one because Dino I change at 3k Synthetic at 6k. More time to ride without worry???Synthetic costs a lot more but from everything I've heard you can go a lot longer between changes??? Flip a coin!!!!