I can't see straight down into the pin but it looks like it should be fine where it is. It is a grid pin and there are two more pins connected to the grid as well. I would NOT use it in positions 1 or 5 however which are the filament pins. Again the blackening is mostly from oxidizing of the silver which was probably accelerated by some heat. That pin may have bee a filament pin at one time and moved BTW. 3-500Z's can get REAL hot with minimal air flow.The best way to clean those old silver tube pins is to remove the socket and dip the whole thing or baste it with Tarnex silver cleaner which is really a mild solution of sulphuric acid. Wash off in clear water after. Either that or dip a Q-tip in silver polish and insert into the pin holder as if it were a tube pin and spin it back and forth and just clean the mating surface of the connector. Again wash any residue off with alcohol or methyl hydrate as it evaporates well and you don't have to worry about getting things wet.
replacement is always the best idea if you can find the parts. Just clean up the old one and keep it for spare parts down the road.
