Hi Alex, Let me also thank you for your knowledge that you share with us. I've only used 15w40 oils in my Perkins. I've used four brands in all. Texaco Havoline URSA, Shell Rotella T, Chevron Delo 400, and now I have Mobil Delvac 1300 in the crankcase. They are all readily available and similarly priced. My question is... do you have a favorite? If so, why. Honestly, don't be modest or PC. Just looking for your honest opinion. Thanks, Mel Knott Sandpiper Chris Craft West Indian 36 Trawler Annapolis, MD