Annual Maintenance:
Oil change, oil filter replacement, ATF/power steering flush if fluids are dirty.
Winterization service which includes basic annual maintenance (Oil change, ATF/Gear oil change, Moister absorber to prevent Mildew, Fogging of engine, Stabil fuel, Complete water drianage from the engine block...)
Adding Sta-Bil to the fuel tank of any boat that is used seasonally, and stored for a season or longer during the year.
Once Every 3 Years: Summerization
Replacement of Spark plugs, Fuel filter (s), cap and rotor.
Impeller replacement (*** Mercruisers with a plastic water pump housing should be replaced once a year).