I have been using Napa Brand Fully Synthethic oil right off the shelf for years. I use same oil in my bike as my truck, wifes car and high hp bikes alike. the oil has never caused slippage, bearings and all parts look like new when torn down for winter freshening ups..I have used slick 50 before in the bikes and picked up et and MPH, don't believe everything you read on the net.. Stock clutches and napa fully synthtic oil, been low 20 sixty foots and still on same clutch pack i ride on the street and dragraced with for 2 seasons..