Who ever said Zuzuski oil was junk ? Mite have said only a fool would buy it at price. But forget the brands of oil, cuz I know there ain't a dimes worth of difference tween'm anyway.
But how does a MFG, or a book, or anyone else, other than the person looking at the dipstick know when oil should be changed ???
You change oil when it starts to get dirty, DUH ???
Or when your Raptor makes your oil so thin, your con rod starts talking to ya !