I am using 5w-40 rotella T6 synthetic. It is JASO MA rated which I beleive makes it compatible with wet clutch applications. It comes in a blue jug and in the USA people are getting it at wally world, in Canada I have only found it at Crappy Tire.
DZ
I've used Amsoil 0W40 ATV Oil in my quads. Love It !!!! It's been great and had no problems. Great starting in the winter and awesome protection in the summer time !! Just my 2 cents !!