[Arran]

This is another case where a T.S.P chassis washing comes in useful, it takes much of the oxidation right off, probably better then baking soda actually. I think that Mike is right, the tube socket contacts are probably brass, or some other copper alloy, with a tin plating, the green looks a bit like tin oxide.
 One of the problems in replacing Loctal sockets is in finding replacement Loctal sockets, so it's probably better to try to work with what you have if possible. There are Chinese made replacements but the diameter and the rivet hole spacing might be different then what Philco used, and everything is measured in Millimeters rather then inches so it's easy to get it wrong.
Regards
Arran