I have twin '05 Mercury Verado 250's with about 700hrs. My last 3 changes have been with Amsoil WCF Marine 10W-40. I was wondering if Mobil 1 15W-50 would be a good 2nd choice. I've done a UOA in the past (not sure what oil) and my fuel dilution was about 3-4%. Should I stick with the Amsoil or just switch to M1 15-50? Merc Calls for a 25W-50 Syn-Blend.