My guess is that it is now a group 3+/PAO/Ester blend.

Sadly, on most of the 300V Ester Core weights, the VIs and TBNs have gone way down. frown
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2000 Z28 1SC 6 speed 165K HARD miles!
Sustina 0W-20, M1 0W-40 (60/40 mix), Amsoil EaO 64 filter
Millers CRX 75-140 NT/4oz. XL-3, RL MTL, 11S