Hi guys I need some advice, I bought a left over 07 mule 610 ,it has a air/fan cooled single cyl engine, it has 7 hrs on it , at 10 I would like to change the oil , I have used Castrol GTX in most everything , it has a snowmobile belt type external clutch , the book calls for the JASO MA spec ,the GTX 10-40wt doesn't have that, would this oil be good ? , also I plan to switch it to Amsoil 10-40wt motorcycle oil , at what hours would this be safe to do, 40-50hrs?