Electrical contacts are a weak-point in any circuit, they are prone to pitting, welding, tarnish, and just plain "hammering" against each other. Other than just replacing damaged electrical contacts, repairs to the contact surface itself is difficult.
Most of the contact surfaces I've worked with are either a solid material, like solid copper, solid copper alloy, or solid silver, or else they are plated, like copper plated with gold, copper plated with nickel alloy, or copper plated with silver.
The plating, if used, is never really thick and can be scratched down to the sub-material if a hard substance like a file or screwdriver is used. Because gold is so expensive, sometimes the gold is only a few molecules thick and can be scraped off using an abrasive material like a "pen eraser" or Scotch Bright.
Plating is put on the contact by the manufacturer. The manufacture uses an electroplating process. Basically, the electroplating process requires that the contact is dipped into a chemical bath solution, and an electrical current is used to bond the plating material to the contact base material (usually copper). The process takes specialized equipment.
There is a possibility that something is available on the web that can be "painted on" using a small paint brush. However, these substitutes for the original plating never work very well, and don't stay on the surface of the contact very well.
A little better than the painted-on fix is a "tin plating" solution. I did use something like this years ago when making printed circuit boards, but the circuit had to be immersed in the solution for an extended time. The circuit board also didn't have any components on it at the time. If there are components on the circuit board, the circuit board will be ruined.
To prevent unseen shorts from happening on attached wires or components with electro-plating or tin plating, an immersion bath can only be used on un-finished contacts.
I've never used the painted-on contact material, and don't even know if it exists anymore. Outside of trying the contacts without the coating, the only thing I can suggest is to replace the contacts.
It may be worth the risk, just trying it without the coating might work.