Not a concern , your right this happens during manufacturing and many NOS tubes have bad Oxidation on pins , you can of course clean these up carefully.
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Unless the pins are rusty, don't use anything but a contact cleaner(like DeoxIT) on them. The discoloration is from heat(not oxidation) and will not affect conductance. Scratching the pins, with any kind of abrasive, or metal bristles(outside of brass or copper), will encourage the oxidation of steel pins. Good stuff: (http://store.caig.com/s.nl/sc.2/category.188/.f) or higher temp (http://store.caig.com/s.nl/sc.2/category.279/.f)
Forgive me! My semantics get in my way at times. The blue/black on the steel pins is actually a type of magnetite, created by heat(and oxygen), during the manufacture of the tube(as previously mentioned). That's a very thin, stable and anti-corrosive layer. A thickness of about .072 micron results in light refraction(per Michael Faraday's observed, "Temper Colors") and the blue appearance. It actually protects the steel from the nefarious, unstable corrosion/oxidation we call, "rust."
Is this magnetite part of the vacuum seal between the glass and the pins?
If it is I understand how a strong contact enhancer could potentially cause problems.
I would imagine that a strong enough solution could possibly destroy the vacuum and thus the tube?
BTW: Thanks for your responses, I've found them helpful.
Probably the best thing to do is wipe the pins down a bit with a clean cotton cloth just to remove any potential oil or grease and call it a day.
The bond of the glass to the pins will disallow the entrance of a cleaner. Folks have been using DeoxiT for decades. Just be certain to use it sparingly and not to leave anything on the bottom of the tube's envelope, that might conduct electricity, or migrate along the top of the tube holder. Personally; I re-wipe everything with Q-Tips, after application/cleaning.