Re: bad seal in lower?
A) Drain the oil
B) Replace the upper vent/fill screw and tighten
c) Make up a rig like this:
Consists of a bicycle pump, "T" fitting, inexpensive fuel/vacuum gauge, and a fitting robbed from a lower-unit fill kit. (NOT the plastic fitting!) You'll have about $20 invested.
D) Insert the fitting into the lower drain opening, make sure the fitting is sealed.
E) Pump up to 10-12lbs of pressure and watch the gauge. Manually spin the prop on the lower unit when testing it. If it holds pressure for a couple of hours , your good to go, if not... re-seal time. If you notice a quick drop, make sure all connections are tight... spray them with soapy water to check for air leaks.