This is so confusing... I thought I'd add more!
I went to my dealer and they were very helpful and open, say for the 195mm axle in my 2012 v8 overland with open diffs (no ELSD) it calls for 5136035AA. That's the "crossfire" gear oil because, they say, it is German... Like the crossfire was... It's a GL4 oil which is not GL5.. But in general means it is less slippery iirc.. It can also effect corrosion levels of internal parts, also iirc from my WRX days..
I'm torn because I think in many ways a gear oil is basically a gear oil and my dealer basically said don't worry about warranty issues with other oils, but a German ZF axle designed for GL4 should really have a GL4 in it.. 45$/qt or otherwise.
Redline 75w85 looks like a good option, but it's GL5 and doesn't say it is GL4 back-compatible.
Not only that, but the above part # pulls up GL4 and GL5 spec stuff on google.. AND my owners manual calls for 75w-85 GL5.
This is just ridiculous.
OK, here's more straight from Mobil oil website:
Question: Clarify Comments on Use of GL-5 vs. GL-4 Gear OilConcerning the GL-5 gear oil, on your website you state the following: "Mobil 1 Synthetic Gear Lubricant LS 75W-90 can also be used in rear axles where API Service GL-4 lubricant is recommended." However, you also say in this "Ask Mobil" section that: "Mobil 1 Synthetic Gear Oil is recommended for all applications where a GL-5 lubricant is specified. GL-5 type lubricants, which have a higher level of additive chemistry, can be corrosive to yellow metals such as copper, brass, etc., and in these applications a GL-4 product is usually specified." Can you clarify this disconnect here? Thank you.-- John Goetz, Newport News, VA
Answer: There are transmission applications that recommend API GL-4 type products where we would not recommend using an API GL-5 fluid because transmissions typically have components made from “yellow” metals. However real axles where GL-4 fluids are recommended do not have “yellow” metal components. As a result, the application of an API GL-5 fluid is acceptable.
So Chrysler may have gone to GL5, and not changed the part number, or all the dealers online are mis-repping their products.. And it looks like a GL5 syn oil should work fine.. So now I'm back to probably going with mobil 1 75w-90 front and rear (as the dealer hinted at using!)..