Thanks for the reply. I'll pump out the old milky oil and add fresh. There is also milky oil settling around the rubber seal around the outdrive. Can that be an indication of something?
Afraid so, prop has to come off, then the housing which contains the seals, which also holds in the final drive, has to be removed. Milky oil on the seal could just be a sign of sloppy work during oil changes or an engine oil leak.
"Don't worry about it too much, modern oils coat the metal surfaces well enough and each droplet of water will be wrapped up in an oil film." That's what I was told by an eminent forum engineer, last year when I made the same discovery. Used the boat all summer. I intended to change the oil seals during the winter. In the end it was not done until the spring of this year. There was no sign of any corrosion on the gear cluster at the foot of the sail drive.
So, if you want to save the lift, do it next winter haul out.