I wouldn't write the lens off just yet. It may well not be fungus. It does attack uncoated lenses but normally cleans off them very well. I reckon I've de-fungused over 40 lenses (thanks, eBay!) and only 2 or 3 have been badly enough affected for the glass to have been etched. Maybe half have suffered some degree of coating loss; the rest show very little damage, and often none at all.
For the Solida, if the metal strip is a tight fit you could rely on friction as Franka did in the first place, but for convenience, and to save taking the spindle out to press it in, you could get it made a slightly easier fit and secure it in place with Loctite - your machinist friend will probably have some or an equivalent.