if the Socket and Fingers are of the same metal, Of which they should be. Not one Tin and other Gold".
You are so right woodchip. It makes me laugh when I see manufactures producing virtually every lead imaginable with gold plated materials. Scart lead for example. How many television sets are produced with gold plated Scart sockets? Unless the materials in contact with each other are gold plated, electrolytic action can occur.
This phenomenon is known in many other situations: Welding, using different materials to that of the host metal.
Plumbing, using brass and copper together. Overtime, the zinc can leach from the brass causing porosity within it. There are many other examples one could no doubt bring to mind.