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 175K miles
Red Line 0W-40/Sustina 0W-20 (20/80 mix)
Fram Ultra filter
Synpower 75W-140/4oz. XL-3
Red Line D4 in the T56