You can use a regular motor oil in the tranny or one of the special racing oils from Kawasaki, Bel-Ray, etc. The racing oils are made to withstand the abuse your clutch and gears take under racing conditions. They cost a bit more, but protect better.IMPORTANT. If you have milky oil then you have water in your tranny. You either rode in very deep water or your water pump seal is leaking coolant into the tranny. This will cause all sorts of bearing problems. Drain the fill the tranny, run the bike and repeat. If you still see the white death then plan on replacing the seal. It's a common thing with water cooled bikes.