Men! Hey I completely forgot about this but ever since I've had my Vstar 650 and recently acquired a Royal Star 1300, I've used full synthetic Castrol oil on them both and have never had any problems with either of the clutches slipping or acting up. And my cousin mentioned it needed to to have that JASO etc. stamp for certain types? Any thoughts or suggestions? Tried looking this up but didn't find the info I needed. Thanks...