Changed my oil yesterday, found the drain plug was loose! I know I'd tightened it. The only thing keeping the plug from spinning all the way out was the safety wire. Since this almost catastrophic event I've asked around and found that the aluminum washer that came with my '03 YZ450 could be the culprit. I've never changed it, never thought I had to. Dealer says the crush washer is only good for 4 or 5 times (or very few) and then it no longer has any elasticity left in it (it is fully crushed) and that allows the drain bolt to back off. Scary!