It might be that the test cock is simply in the open position. They are quarter turn ball valves, opened and closed with a screwdriver. Check to make sure it isn't open, a simple turn with a screwdriver might fix the problem. If it truly is leaking, it is just a matter of unthreading the old test cock, and threading a new one in. Also, if it is only 6 months old, it should still be under warranty.
Tony Posey
Ridge Run Landscapes