I took an old drain or fill plug and drilled a small hole in it then inserted a basketball pump needle in it and sealed it with RTV. I cant give you numbers but the internal pressure should stay low say 2 or 3 lbs of pressure. I submerged the lower unit and pumped some air into it to find a leak in my gear housing. Problem with pressure testing is it dosent always work. I have seen a burred drive shaft at the seal not show a leak until the motor is running. The RPMs on the shaft will allow the pitted or groved shaft to allow the leak to happen where when the shaft is not moving the seal will hold. Worse leaks I have had is at the drive shaft seal and at the prop shaft seal. Hope this helps Good luck.
I think the manual calls for 10 psi on an empty unit and hold for 1/2 hour without dropping.
And Euro is correct: That does not necessarily mean it will not leak under operating conditions--but it's a start. If it doesn't hold pressure, you know it will leak.
