Castrol Syntex, while a good oil, is a Group 3 not a full PAO like Redline or Amsoil IIRC. Even Mobil 1 is likewise. "Full Syn", "True Syn", bla, bla bla is all unregulated advertising hype.
Synthetic oils
A Defining Moment for Synthetics
Synthetic
Synthetic Motor Oil Gets All New Semantics
Synthetic oils
A Defining Moment for Synthetics
Synthetic
Synthetic Motor Oil Gets All New Semantics