Johnson 1965 6 hp. Foamy gear oil at end of season. I would like to do a pressure test to find where the leak is. I did replace the bearing seal and gear case seal. Still leaked. At this time I would think that the shift rod o ring is the suspect. I put together a pressure tester I cobbled together from components from the Home Depot and the yellow fitting is from a gear oil pump kit. Having never done a pressure test before my question is should it be done with oil in the case or drained. I can submerge the lower unit under water and try to detect air bubbles. What is a good pressure that should be held. The tester goes to #15 and I will use a hand pump to pressurize.