My understanding is it’s recommended for certain applications such as hypoid, spur, bevel, helical, spiral-bevel and worm gears in differentials.
As to why I still don’t know. 💩
Synthetics typically out perform mineral (conventional) oils.
I’m installing a Strange S-Trac helical gear differential in my 2014 Mustang GT. Strange recommends petroleum-based 85W-140 with no added friction modifier. They state synthetic gear oil will adversely affect unit operation and void warranty. Would additional wear or improper operation occur if...