I too have expierienced a loss of coolant. I have already replaced my clamps(crap, for sure!) I guess I don't know where it's going. I keep my bike in a heated garage and have noticed no leaking coolant.
Bad head gasket? I don't know and it didn't seem like enough to worry about, but it was about half of the overflow tank that came up missing. I really haven't checked as often as I should. I have already had a pinhole in the rad from a rock shot, but successfully repaired that. It could be a leak that only appears when hot.
Keep us posted,
2002 Yamaha PW80 don't break it dad!
1996 Honda XR250R just right.