Little confused about what type of oil to put in the crankcase. According to the manual its says use SAE 10w-30, which is a typical car/truck engine oil. I called a marina today and they said never use that type of oil. He recommended M4 which is a oil designed for Yamamha 4 strokes, which is the type of outboard they specialized in. I have a new Nissan 15hp 4 stroke. What kind of oil do i need?