I've seen Magnesium components cause (or almost cause) a fair bit of vintage heartbreak over the years.
* I was standing taking photos on the inside of turn one at Nepean back in 1993 when the great Roy East crashed his Metisse coming into the corner. He hit the deck so hard that I thought that he must have been either killed or at least badly hurt. Luckily Roy was a tough old bugger and he escaped the accident wit nothing more than a headache and some missing bark. When we picked the bike up we discovered that the magnesium Rickman front hub has shattered like a broken bottle when Roy grabbed a handful of front brake.
*I was waiting at the pit gate to go out for a race at one of the early vintage meetings at Amaroo Park. While checking out the sidepipe CZ next to me I noticed that the spoke flange on the magnesium front hub was cracked almost the entire 360 degrees...only a 20 mm section holding it all together. I tapped the bloke on the shoulder and told him but he wasn't that interested, he just wanted to race. I had to actually get off my bike and physically draw his attention to the hub. When we later had a closer look, the hub had about 5 other cracks that would have spelled disaster the first bump or jump he hit.
*Broken Hill Racer Robbie Tumes crashed his brains out in practice at the 93 Kembla Nats when the mag backing plate on hos '74 KX250 shattered like a broken plate.
* At the same meeting Jason Cater holeshot the pack on his Maico and when he hit the front brake the magnesium backing plate exploded in an almost identical manner to that on Robs Kawasaki. Jason hit the deck and took out half the field, calling for the race to be stopped and restarted.
How many mag Honda water pump housings, early YZ clutch covers, XL Honda clutch and ignition covers and other parts have been trashed over the years? If those parts had been made from aluminium they'd probably still be in use. I'm that wary of the stuff, it's preventing me from using CZ hubs on any of my project bikes, despite their superior brakes and light weight.