I just put fresh Delo 400 5w40 CK4 in my JD 425 water cooled Kawa engine, I feel it or the dino version 15w40 is just bout the best without going overboard on something expensive like Redline etc. and certainly all that's needed, and probably overkill to a minor extent. There are those who argue that 30w or 40w straight grade "small engine" oil is the best for a couple of reasons, (according to the manufacturers) it has foam inhibitors, and a bit higher zinc, and some other small engine attributes. I dunno what exactly is the best, but I feel like this is plenty good enough. From all the VOA/UOAs I've read, there isn't a huge difference between HDEO and small engine oil, even though the manufacturers would like us to think there is. It's hard to know what's best, with all the hype, and advertising, and the manufacturers have their axe to grind with sales, so I just take an educated stab and go with it. One things for sure, an air cooled Briggs or Tecumseh, will last several lifetimes with almost any oil under the sun, and never changed!