These very rare, not to mention expensive 906 center-lube Magnesium chainbox housings and covers have seen better days. Over the last 50 years, the Magnesium progressively deteriorates unless it is properly treated. This is what happens to the Magnesium if neglected and left untreated https://pbase.com/9146gt/image/155999167 and in this photo you can see a remarkable improvement after a careful media blast and tumbling https://pbase.com/9146gt/image/156922484.

Believe it or not, these are the very same parts, but finished with the Chromate process https://pbase.com/9146gt/image/157186223 Nothing short of an amazing transformation!