powerstroke

Sorry for the sophomoric question here. I ended up with this 2.5 gallon jug of 15W40 400 SDE on clearance for less than the sticker price. I know it's not blessed with the Ford specifications. My owners manual states to only use API approved symbol/CJ-4 motor oil, which it is. Would you happily...

I have always used delo 15w40 conventional. Since they won't be making it anymore should a guy use their synthetic blend and will it really hurt the seals and gaskets switching? I read an article by delo a bit ago stating that their conventional oil was better than others synthetic blends...