Well I dread the day Amsoil or Redline starts monkeying with their products!
I can afford their 15W40 full synthetic on the 603 engines because I push it to 5000 miles between changes. I once did 7500 miles and although the analysis came back ok, that mileage occurs over 16 months in one car and longer in another so I figure its been in the crankcase too long so I change it out anyhow.
FWIW Chevron changed DELO 400 in the past 6 months but I still buy it for the 617's. To my nose it smells like it has less additives in it, maybe are the oil co's are trying to give more for less.
I wish I had bought several cases of oil a few years ago before all the price increases.