I bought about 10 of them for my personal use back before Y2K. I've used up 2 and the flints still work fine but the magnesium is down to a nub. The rest are just fine sealed up. I don't think magnesium corrodes. I'll have to look that up.
A clean, unprotected magnesium alloy surface exposed to indoor or outdoor atmospheres free from salt spray will develop a gray film that protects the metal from corrosion while causing only negligible losses in mechanical properties. Chlorides, sulfates and foreign materials that hold moisture on the surface can promote corrosion and pitting of some alloys unless the metal is protected by properly applied coatings. The surface film that ordinarily forms on magnesium alloys exposed to the atmosphere gives limited protection from further attack.