VFR - I was talking to some guys from East Fortune a couple of weeks ago who were telling me about the problems they're having with old instruments and radiation. If I remember the conversation correctly, the main thing to look for is whether the luminous painted markings on the face are still solid, or the luminous paint has started to crack, or it has started to crumble and you have lose paint dust inside the instrument.
If the paint has cracked or crumbled, don't mess about with it, but ask for advice about what to do with the instrument (sorry, haven't got a clue who you'd ask though). Apparently the radiation is contained within the paint, and is okay until it starts to break up. Hope this helps.