I just started experiencing clutch slippage under hard WOT accell in 3rd, 4th & 5th gear only after re-jetting carb and poormans BAK to stock airbox and stage 2 stock exhaust mod. All was good last fall before the winter mods. The oil in the engine was Yamalube from the dealer when they did the trans recall last fall (I had Ams/Oil 20/50 in it from when I first purchased the bike). I tried the seafoam treatment in the oil last week and though there was an improvement it still slipped a bit. I changed out the oil and filter today for my usual AmsOil 20/50. We'll see how this goes. My 99 only has a little over 17,000 miles on it but I have been reading on issues with the factory weak clutch. It works just fine under normal everyday easy riding. Just the extreem "Get On It" runs is when it slips. BTW, I am and have been only using the motorcycle AmsOil.