your engine oil works the transmission, best to use yamalube 4 or valvoline atv 4 stroke oil. given the age of the bike, it's probably do for some clutch work. maybe a new clutch and pressure plate...take the clutch cover off and jack it up securely on jack stands and run it, you should tell where the noise is coming from. in the service manual, you can only turn the clutch clockwise, try turning it counter-clockwise and if it moves, it's shot. also look at the front sprocket and the gears for wear.