Plug off your breathers and dipstick. Mine has a vacuum pump so no breathers to worry about. The dipstick is O ringed so it seals. Grab yourself a handy dandy Harbor Frieght regulator. This one was $7. Attach the hose to the valve cover at about 5 psi. Spray away with the soapy water. When the trans was pulled for service there was a little oil at the bottom. Just a few drops at the bottom of the bell housing. Once the trans was out everything looked dry. As always this method finds any leak.
Doug