I have a big westerbeke genset in my boat, the impeller is a jabsco, the oil and fuel filters on the engine I get from my special suplier, the belts an automotive product, the main engine is a 3 cylinder mitsubishi unit, so the only service part from the makers is the anode in the heat exchanger.
I am on it today, however water hoses and thermostat housing are on the list, I suspect they are Westerbeke only, so Credit Card out and poised..... for a battering!