never heard of Mercury oil causing problems in Johnrudes, how does it know its being put in a competitors motor? I know Kekifer and Buckley were pretty competitive, but viral oil is pretty inventive. Serioulsly, all three outboard manufactures will tell you if you can't run their brand TCW3 oil( in normal carburated or EFI twostrokes), at least run an outboard manufactures oil. All the outboard manufacturs have their oils made to proprietary mixes by oil manufcturs, I've found Quaker State shipping statements laying in the bottom of OMC and Mercury oil crates, seen Bel Ray invoices that came with Mercury gear lube. ANyhting that meets TCW3 specs is supposed to be OK in a carb or EFi 2stroke, but Penzoil and Lubrimatic don't build engines, and are not worrying about warranties, to keep their product priced competitive, they are going to meet the minimum specs for TCW3 and leave it at that. The outboard manufactures tend to go beyond the minimum in their blends to help make their engiones last. As far as high performace goes, Klotz or Belray, that oil makes power( seen it proven on a dyno). If you are running a DFI( opti, e-tec, or HPDI), i wouldn't run anything but the best oil the engine manufactures provide for their specific engine, those motors are runing on the edge, a little too much ash or carbon build up can make those motors go boom! I recomend some type of decarb( seafoam, carbon guard, ringfree) in every tank, especially if you slow troll. the local water taxi has put 3000+ hours on their 4 stroke 150 Yamahas, have run ring free in every tank since day one. I have checked the valve clearance every 1000 hours, haven't had to change anything.