I found this thread on a Ducati site.
https://www.ducati.ms/threads/paint-damage-magnesium-wheels-stress-cracks.30235/It seems that magnesium alloy would not be a wise choice for longevity without regular expert inspection once past a certain age. Seeing what's happened to yours it would certainly put me off buying any that were from the Fulvia days. That said, has anyone ever heard of one failing?
My wheels are FPS (a factory option) and I'm hoping they're aluminium alloy!