Hi no there is no sign of any discolouration, rust or anything on the socket itself. I would say the stains on the tuners look almost like dried milk type of thing but cant say how it would have got there??? These would have been under the sealed lid so a bit strange.

I spoke with the repair company linked earlier in this post. Lovely guy called Martin that I sent photos of the inside too. He said the circuit board is showing signs of damp and he doesnt think the signal problem is anything to do with the tuners. In his experience the tuners are marked from some metal corrosion and not from something leaked on them. As he probably has tons of experience with these issues he knows all there is to know. It has been arranged to return the box to them, he is not sure if it can be fixed or not. Depends what they find the fault is but he seemed to have an idea. He said he will update me once they have examined it. Worse case scenario I have lost the postage for a unit unfit to use.

The woman I purchased from has it sat her in garage but didnt know how long. Lesson learned not to store anything with circuit boards in the damp.