I think I would make a tester with a LED and a 1k resistor with an F connector on it. If you have enough current to burn out a balun in a splitter, it will light a LED. Then just start plugging in into boxes until you find the one with the leaky RF can.
Use a bi color 2 wire LED, then you don't care about polarity. One way will be red, the other green and AC will be yellow.
