Keep up with the routine maintenance
Change the oil every 50 hours of engine use and before laying the boat up for the winter. Acids build up in the oil and these will attack your bearings if left in the engine over the winter.
Change the water pump impeller annually, preferably in the spring. The rubber blades harden over time and pump less efficiently (possibly not at all). Even worse, they can break off and lodge in the cooling passages of the engine. It's better to change it. Be sure to keep a spare on board, in case of emergency. You can't run the engine without it. By the way, the impellers can harden even if they've never been used, so keep your spares fresh.
Tune up the engine annually. This is mostly a matter of replacing simple parts, and can be easily accomplished even if you're not a mechanic. I recommend replacing the spark plugs, points and condensor every year and the distributor cap, rotor and spark plug wires every two or three years. Keep spares of all these items on board at all times. Also, you should have a spare coil. If you have a fuel filter (which is highly recommended), make sure you have a spare filter element, too.
If you need more help or other parts
The first stop should be your local dealer. Develop a good relationship; it'll be worth it.
If you don't know your dealer, you could call the closest Westerbeke distributor to find one. Or, contact:
Westerbeke Corporation Avon Industrial Park Avon, MA 02322 508-588-7700 Fax: 508-559-9323 WTBK@aol.com
And be sure to check out the Collaborate pages for up-to-date links.