source if its good

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Yeah since Mobil 1 is not a true POA base synthetic anymore. They sued Castrol for using Hydrocrack, not they are producing the same quality oil. I've been running RP for a while now. It keeps my 4.0 at N.O.T. and it's a true POA.
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96 4.0 AX15 HP9", D44, 4.88's, Detroits, 37's

I did email Mobil, it'll be interesting if they reply at all and if they do what they say. Probably just marketing malarky.

To meet the demanding requirements of today's specifications (and our customers' expectations) Mobil 1 uses high-performance synthetic fluids, including polyalphaolefins(PAO), along with a proprietary system of additives. In fact, each Mobil 1 viscosity grade uses a specific combination of synthetic fluids and selected additives in order to tailor the viscosity grade to its unique requirement. Mobil1 motor oils are still 100% synthetic in formulation.

-- Thank you for choosing ExxonMobil products.
If you need further assistance, please contact ExxonMobil at 1-800-ASK-MOBIL

-Matt Jacob"

Seems to say they're still at least a percentage PAO oil but not much else.
If you were using it in an engine where lack of ZDP would be a problem it'd be smart to run frequent oil analysis until you were convinced the engine wasn't eating itself...