Flat Tappet Lifter Oil ??

I use the Shell Rotella T 15W40 and STP. Did a cam swap last winter and didn't see any wear on the old solid cam and lifters (3 years) Comp Cams 263/267 @ .050 648/660 lift. I went with another cam with more duration. Did lots of local car shows, cruises, and no more than a 100 1/4 mile passes at the strip.