Hey everybody - So our family has a 2007 Mercruiser 4.3 that I was asked to get oil for. My father in law said that he talked to the guy who rebuilt the engine and he said to not bother with getting 20w-40 mercury oil and to buy a good straight 40. I found a decent price for some Rotella 40 and wanted to ask if any guys use this for their boats and if it is a good product. I know the 15w-40 is widely accepted as a good oil and many use it in their boats but what about the straight 40?