Some of the "patina" on the case hardened bits could just be oil, dirt, and crud. Have you tried wiping with something like CLP, then progressing to mineral spirits, alcohol, lacquer thinner, and acetone? Keep solvents off the wood, but solvents should not harm the case hardening or the associated colors. It is possible that the metal was coated with something to protect the case coloring, perhaps linseed oil or lacquer. Both of those will get darker with age and the linseed oil can have a tendency to hold surface dirt.
Some old threads here and elsewhere have suggested polishes like Flitz to clean CCH surfaces, but I don't think I'd risk it without a test on an old beater.
You might also try a stainless steel scouring pad with oil to gently clean the CCH surfaces. I have used it with some success on lightly rusted blued and CCH surfaces.
