Sadly Hampster, your hub is rooted. You could weld it but would you ever trust it again? I certainly wouldn't. Unfortunately, unless magnesium has been well looked after from new it ages poorly and actually rots away, sort of like wood. Moisture and the elements are not magnesiums friends! I witnessed Roy East nearly kill himself at a Nepean vintage dirt track during the early 90's. When he grabbed a handfull of front brake for the first turn from the start, the magnesium hub on his Metisse shattered like a broken plate bringing the old champ down at speed where he was then cleaned up by those following. Very, very ugly.
Another mate was tightening the spokes on his CZ a few years ago and on the last tighten of the spoke the whole hub flange broke away with a really loud bang. It scared the shit out of him but not as much as if it would have happened on the track!
I got a magnesium OW Yamaha front hub with my Boyd and Stellings Suzuki and even though I wanted the bike to be as trick as possible, I couldn't bring myself to use that hub. I fitted an aluminium version from a YZ 125X and now have no worries about it exploding while one of my 'hired guns' are racing the bike.
