[The Philpott]

..The wander plug sockets can generally be cleaned up as Phil says, sometimes i have resorted to 600 wet & dry wound into a cylinder shape where they are very grotty. The split pins have a small contact area of course, such that a little patch of (a real pain to shift) verdigris or dezincification can upset the readings.. some avominors have 'twizzle' marks on the bakelite where people have spun the terminals round in frustration.

Dave