I got my LEGO from storage from when I was a kid (1980s) and while almost all bricks are in good condition, the Technic axles are in a pretty bad shape. They seem to have corroded(?). Please see the attached picture. This has happened to almost all the axles but with different degrees of severity. None of the other bricks, technic or not, black or not, has suffered this.
Any idea what might have happened and how to prevent this?
EDIT: They were stored in plastic bags sorted by color (one bag per color) inside a larger canvas bag in a non-lit, dry environment (garage). All other bricks seem to be fine, regardless their color. Stickers that had been applied survived very well (bright colors) and still hold strongly. Once I got the collection back I mixed the bricks and ran them under warm tap water and let them dry on a towel on the floor for a day. These were the only bricks that were affected.