[mikethedruid]

First thing I would check is the socket of the bulb itself. If the rubber is dead in it, it may not be making a good contact once it warms up and things expand slightly from the heat. Cold, the bulb will make a solid contact, but as things warm up, the metal and other things expands, and the bulb become slightly loose. Try tapping the light socket with the radio on and warm, and see if that causes the problem to appear. In any case, if you have not rebuilt the socket, I would do so.