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I'm not sure what you describe as leaking onto the starboard motor mount. A picture might help there. In the meantime, allow me to tell you some facts of life. Every drop of oil that you put in the gas goes through the motor and comes out somewhere as it runs. Some is burned and comes out as smoke. Some goes right on through and goes out with the exhaust and cooling water discharge. The second scenario often (but not always) results in a foamy, emulsified goop. I assume that is what you are referring to.
There is a third discharge route and it is right next to the lower crank seal. I am attaching a couple of pictures showing that discharge route. As the motor runs, especially at slow speeds, oil tends to settle in the crankcase (think puddle). That puddle will make it run terrible for a few seconds when you accelerate. As a fix, they provided drain valves to get rid of the puddle. The pictures show where it goes--out right next to the lower crank end. From there it goes out the exhaust, along with and adding to the previously mentioned. glop. The second picture shows a modification made in 1968 where they re-routed the drain to go directly into the hot exhaust to hopefully be dealt with without making such a mess.
Do I think you have a bad seal?? I have no earthly idea. Maybe you do and maybe you don't. Either way, you must understand that oil discharge is normal. 50 years ago, everybody understood and accepted that. Now, in 2015 everybody looks at it and says OMG! If you can't live with it, antique motors probably are not for you. But they are a great hobby for those that understand and accept that the world won't end because of them. Hasn't yet, anyhow.
Waiting on the motor mount picture...
