heres my problem, im using motoul 5100 oil and everytime i replace the oil it lasts no more than 2 rides before it is completely black. Im riding an 08 yz450 with about 90 hours on the clock. I ride motocross and i don't think that i ride the clutch a lot. The bike has had no engine modifications and i replaced the clutch plates just after i bought the bike second hand. The guy before me was running no clutch freeplay and this burnt out the clutch. I have been having this problem for a couple of months when i done a woods ride and was really reliant on the clutch trying to get up some slippery hills. Any one know the cause? Please help?