Water in lower unit?

[steplift20]

I think I'm getting water mixing with my lower unit, today and last year I noticed that when I drain my lower unit oil it comes out a little milky and a very light green and dark normal green if the seal is no good ,what and where are the seals? Are they the ones under the water impeller housing, I never did that before and don't know if I should bring it to my mechanic or try it myself ,it's a 1988 150 Mercury outboard, any help would be great thanks for any comebacks. I live in New Jersey I do have a mechanic but he is not as good as he used to be not his fault he go screwed really bad but that's ab other story