Ive owned Polaris's since 1993 before they were cool. Most were two strokes, and I still have some two strokes. But I have a Sportsman 500 HO and a Sportsman 700 twin. I use Castrol Syntec 5w40 in the 500 HO (If its good enough for Porshe its good enough for a quad) I use Castrol GTX 10w40 in the 700 and its super smooth and actually quiter then the Polaris factory brand oil was. Polaris Sportsamn dont need a complicated oil, they have no wet clutchs or anything "weird" going on. They dont require anything but a high grade car oil. They duplicate the same thing that a car oil does and the same job description. Although in a harsh enviroment, if your like me and change it ever year, its not like its staying in there for even 3,000 miles more like a couple hundred so anything will work. The chaincase is a different story, Ive heard of people useing 5w20 motor oil in there and I know when Polaris first came out the speced 30 wt oil in the transmission then started selling special oil for $11 a qt. No trouble using 30wt, 5w20 or Polaris oil. Ive used all three in the two stroke transmissins without problems but for the 500/700 I just use the Polaris Syn and pay the $11 a quart once a year.