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Sounds like the car may have had some restoration, and someone tried to make the relay link look like "as forged" with carefully selected paint color. Originally, the relay link was a blueish-grayish, scaly looking finish, or some of them were painted black. Your "off-blue" finish has to be paint in my opinion. I can't imagine a natural relay link still having its original "as-forged" finish after all these years...humidity alone would turn it rust red.
Duplicating this "as forged" finish with paint is impossible in my opinion. You are left with cleaning it up to it's natural finish (bead blast, wire wheel, etc.) and applying a light coat of clear, OR just take the easy way out, and paint it black. I don't remember the judging guide saying anything about the relay link having black paint, but I worked with a Master Judge at one meet, and the black relay links sailed right through...no deducts. I even raised the question, and he said that some relay links were painted black. The same is also true on the control arm shafts...some were natural and some were black, and there is no way to tell which the car had originally. A good restorer will try to restore the car to its original finishes as faithfully as can be ascertained, even if it means taking a minor deduct.
If by some miracle, it turns out your finish is really "as forged", I would do nothing but carefully degrease it and apply a light coat of clear.
Upon closer review, the centerlink is NOT painted and NOT rusted. It appears to be a natural finish that is grayish in color (more gray than blue). I can not find any signs of paint. However, it does look like it was cleaned to the bare metal and given a nice coat of clear. After reading your post I know believe it is "as forged".