I have an 2001 XR650 that I ride the hell out of. I blew the shaft seal out of it a few months ago when I was riding through some tall grass. It got a bunch all wrapped around the chain and gouged it out. I had it replaced and since then I have ridden it a couple times on the trail, and one rough weekend at the dunes. I just had it back out to the farm and was riding it around and the seal blew out again. I have not torn it down yet but I am just wondering. Is this normal for 650's to have them go out this often? Could the sand have made it wear prematurely? Second question: How hard is it to do? I had the shop do it last time because I don't know a whole lot about the four strokes just yet. I have re-built many CR500's and CR250's. I just don't want to screw with this thing because of how reliable it is. I looks like you just take the sprocket off and swap out the seals? Any help is greatly appreciated.