I'm now due for a new chain/sproket on my YZ450F '04. That's something I don't really know a lot about, all I hear is O-Ring and now X-ring. What's the difference?? Another thing, how many teeth should I get for sprokets? I actually don't know how many there are on stock ones...but anyway, I found my 1st gear too high and my 4th too low. What can I do? Tell me what you bought and how it feels, tomorrow I'm gonna go order this stuff. Thanks.