The rollers get gummed up (and worn too) after awhile and they need to be serviced with anti-seize... messy. SS is right, they are on the left side of the motor. When Madmatt300 was on it, and it was ridden hard, I had to do it once a year or so. There is really no big deal about working on this side of the motor, just disconnect and plug the oil lines to remove the cover completely; as the oil pump is on this side. Its been awhile since I worked on this motor since my 6 year old is putting around on it now... But, I think you'll need an impact to remove and install the clutch nut. The seal will probably be okay to re-use. There are lots of tricks to do to this motor and clutch as your kid gets more advanced.... I wish I had all the e-mails still detailing them. Oh yeah, you can prolly re-use the gasket, but if its bad, replace it. The belt hates water!
Honda, Best On Earth
2000 400EX, 1996 300EX and a 1997 LT80 - each with a bunch of custom schtuff on'em!
2001 CR250
2002 KDX220