I just bought another boat (1982 Hunter Cherubini 33) and am going through the routine maintenance. I downloaded a couple of manuals and if I am reading them right, the gearcase takes the same oil as the crankcase or 30W motoroil.
I would appreciate it if any of you Yanmar2GM owners would give a big "Amen" on this or tell me otherwise.
I read through the manuals as well and concluded that I should use the same oil for the gearcase and crankcase: 10W30. Take my opinion with a grain of salt, though; I did my first dieselenginemaintenance chores last fall, so my hands-on experience is quite limited.