I have a feeling that nut is still somewhere in the top end. I don't know if it would even fit through the oil galleys back to the bottom end. If it did, i still wouldn't worry about it too much. When I was replacing the clutch last year, I happened to peek through one of the channels into the sump, and found a washer just laying in there by itself, that apparently had came off the shift shaft from a repair the previous owner did. And I think there's still another one in there, but I can't find it. That washer was in there for over a year through mx, xc, wheelies, and everything else, and never interfered with anything. Just make sure that nut isn't in the top end, then I say get another one, put it back together, and cross your fingers. If she blows, then you got yourself an excuse to get a rappy.

 

I put it back together and its still making that noise so i dont think the fell through to the oil pan. Ithink it needs a new top end because even with the valve adjuster adjusted all the way down theres still an 1/8 to 1/4 inch of room between the rocker arm and the valve.