Dead Dinosaurs. that is the stuff to get. The synthetic dosent stick to the gears all that well. At least in the older stuff we run, the Dinosaurs help the transmissions shift.
The rear diff likes it as well.
Cheaper the better.
Amsoil in the engine, 15w50 racing Amsoil 2 cycle oil as well, buy it by the gallon at the snowmobile shops
Plain Old gas 87 octane. and run the primary rich