All oils have the api rating on them. There is a standard for all countries called ISLAC and the oil that Nissan uses for the Z is a ISLAC GF-6. The Mobil1 that we all get off of the shelves is ISLAC GF-5 because it does not contain ester. Ester is a additive to the oil that helps limit the audio noise that comes from the valves clattering. While not using an ester based oil does not damage you car it just gives off the sound of your valvetrain. From what I was told by the service manager who is very knowledgeable about the Nissan oil, he stated that the Nissan oil is infact purchased from Mobil1 but they add ester to it and also put their name on the white bottles. Hope this helps you out.
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