Engines can't read the labels on the oil tin
but they do like regular changes though, every 1000miles for my Huntmaster and after 10000miles or so since SRM rebuilt my engine it seems to be getting better.
I de-coked after 7000miles to stop a little pinking (successful) and everything looked very good. Tappets still spot on.
But I must say it's not the oil that SRM recommend. They say that a straight 40 is used without any filter.
Maybe the answer comes in a few years time when I have done 50000miles. I'll report back every 10000 miles