[willy]

On a previous motor of mine the lower unit had been serviced just before I bought the boat. Being foolish I trusted the mechanics work and just checked and found the oil clean and ran the boat half the season before I checked the oil and found it was all milky looking.
I changed the oil, and replaced the washers which should be done each time and were not, ran the motor the rest of the year and each year after and no more milk.
It was the washers, also if you have a mild leaking seal somewhere there are some fluids to put in your oil which will seal the leak and they do work. I can't remember the name of it now but according to a marine mechanic it does work well unless the a=seals are just boken or rotted bad, good luck