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Agree with you.
Whatever you beleive this varnish is, it should not be there and should not be removed with steel wool whatever the grade, as steel is harder than copper and gold and may remove some of the metal.
Instead it would be Wise to first start with different organic solvents, from Alcohol, through IPA, to Acetone, to see what is needed to remove any organic layer that may be there, NaOH can also be tried since it does not aggress copper or gold.
As pointed out the contacts must be gold plated. If they are no longer gold plated, it looks like someone has removed it before you, probably with a similar brutal abrasive. And bare copper does oxidise quite rapidly
But no problem: once you have removed any organic residues, you can plate the copper with Gold again. There are kits available. Usually you start with an activator that removes oxide residues, then you apply a layer of Nickel and finally gold. All this is nowadays available for electoless plating, so no need to send a current. Once you have a new gold layer you can be sure it will last for many many more years.
Good Luck!