As you read the labels bear this in mind; there is no API engine oil grade that implies an ability to retain viscosity in extremes of shear, such as a gear lube would experience, and so, there is nothing you can learn from any of those grade specifications that will give you any information as to the oils durability in that regard. JASO MA/MA1/MA2 are supposed to include some measure of consideration for this, but even the actual presence of the words, "Certified JASO MA" don't necessarily give you an indication of anything more than the fact that the oil is an equivalent of API SG/SH, and is suitable for a wet clutch. The only thing I have seen on anyone's label that definitively states that the oil inside can stand being a trans oil is "API GL-1", indicating the oil inside is, among other things, a legitimate 75w-90 gear oil (the SAE grades for gear oils are different that for engine oils). This appears only on the label of Amsoil MCF and MCV to the best of my knowledge. Otherwise, your stuck with either published lab tests or your own UOA's to find out. .........No I'm just kidding. If I'm understanding you correctly, even though they meet the API and JASO requirements previously mentioned, without the API (GL-1) label there is no way of knowing exactly how long the oil will last/retain its required viscosity when used as a gear oil.