Just got an RT3.
I've been riding and racing since 1972. I've had over 300 bikes but most were Yamahas. My first one was a 72 JT2MX. I currently have a 1978 Yamaha DT100, 1978 DT175, and a 1973 RT3 360 along with my KTM, Husky, Ducati, 2 Hondas, and a couple Honda vintage 3 wheelers. My RT3 is one ill restore to pristine, plate it and ride it on and off road.


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Hello Steve, and welcome to the forum
Oils have changed a lot since the days when these vintage Yamaha Enduros were made.
What's most important now days, isn't which weight of oil you use in the transmission case (30wt or 10/30wt), . . . it's that you use an oil that is designed for use in "wet clutch" applications. If the bottle or can doesn't state "For Use With Wet Clutch's" or, ... carry the JASO M1 or M2 rating, then don't risk using it . . . otherwise, you'll risk that the clutch plates will start slipping.
As for the oil tank, that's tucked up under the left side of the seat, definitely look for a product that says something like: Two Cycle Oil, or ... 2-Stroke Oil ..... better yet, If the container says ... For use in oil injection systems
Probably easiest to find if you visit any one of the Japanese brand dealerships. They'll likely have a variety of oils that are appropriate for you to choose from