Thanks. Can you give me a rough idea of how many quarts of oil to buy. I am helping a friend. It is his first boat. I have never changed the oil on a 4 stroke. I assume it is similar to changing a cars. Is there a generic type of oil or does it have to be mercury. Will say 10w 30 work? Also where will the drain plug be? Sorry I don't have the serial #. My friend has the boat. How often should he change the oil? Thanks for any tips