Looking much better and again safe to touch - no longer 'icky' and brown - well worth the effort :)
Additional to cleaning, two defects of the keyboard were remedied - with support from Hammond nr. 90210.
The first issue was the broken FIG key-top. The keys have a paper insert under a glass cover, however on the FIG key the glass cover was missing. Judging from the state of the paper label, the glass must have been shattered and lost decades ago.