is your diff breather clogged up?
is the arb fitting on the outside of the housing hooked up? the main brass plug into 3rd, o-ring, and inner fitting? . it sounds like the diff breather is clogged and it is pushing the oil through the o ring on the carrier and out the air line on top.
Whith the breather out it still leaks. I don't have an airline hooked up yet (waiting on a compressorr). How could oil leak in to the ARB? I bought the 3rd second hand so I would bet it is the old style, if that helps. Would the thermal expansion of the oil push it into the ARB and out the tube?