Synthetic oil. When I did my first oil change at 580 miles I took a look at the stuff that came out. I can't say for sure, but I don't think the oil was synthetic. There was no doubt that the oil was laced (it stunk) with sulphur. They put that in there to help with the gear box break-in. I started with advanced Amsoil 10W-40 high performance engine and transmission lube on the first change. This is my subjective feeling, but I think the engine was still building HP even after 10,000 miles. Subjective. If you check the owners manual you will see that oil change intervals are 7500 miles. They assume that you will use a fossil oil using their specs. Don't have heart failure, but I leave my synthetic lube in for 25000 miles or 12 months, whichever comes first. I also use the Amsoil Ea 303 filter that pulls down to 15 microns. My first change in 12 months came at 12,275 miles. During that period I did not have to add any lube. I run a dual filter by-pass system on my GMC Duramax Diesel that pulls down to 1 micron. Oil really does not so much "break down" when it goes south; it becomes contaminated. The filter that you use is as important as the type of lube that you use. I saw a very pretty machined lifetime filter for bikes ($89)that would only pull down to 40 microns of crap. I would not put that filter on my bike. Amen.