If you take a regular add pack like you miht have seen in the last ten years (say it was coomon during the SL, SM era) and you add that add pack at the stndard treat rate, to a gallon of gp.1 or 2 basestock, is the resulting fluid sufficiently different from te starting base to be called a 'synthetic'? If it doesnt appear that way in nature its syn, right? So we have all been using syn for all of our lives because whatever gets drilled out of the ground is filtered, de-waxd, additivised and then put on sale. Or do you mean specifically grp4 and grp5? Unclearly defined question is unclearly defined.