Usually once a season. The book calls for every 50hrs. This is a 1991 johnson 140hp. I do it before it freezes so if there is any water in there I can get it out and I don't have to worry about blowing my seals.
I do once a year. I bought 5 gallon pal of Yamalube. Can this gear oil be used in the front transfer case of Honda Ridgeline that requires front transfer case, Hypoid Gear Oil 80W GL4 or GL5?