350 Chevrolet flat tappet cam Boat is only used hot summer months and Mercruiser recommended straight 40W for ambient temps above 60 degrees F. I have fairly easy access to Rotella 40W, Delo 100 40W and Delo 400 40W. I heard that the Delo 100 has less ash than the 400, is less ash better for my use? Which of these oils has the most zinc and additive protection for the flat tappet cam? Which of these three oils would you run? Thanks.