Now --- When I say even EATON is confused.....
This is copy and pasted directly from their FAQ page on their website for their rear ends:
http://www.eaton.com/Eaton/ProductsS...ials/index.htm
Detroit Truetrac
Q: What kind of oil should I use? Can I use synthetic? Do I need friction additive/modifier?
A: A quality petroleum/mineral based oil works best in the Truetrac units.
We do not recommend synthetic oil. Friction additive/modifier is not required.
Eaton Posi
Q: What kind of oil should I use? Can I use synthetics? Do I need a friction additive/modifier?
A: Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance.
Detroit Locker
Q: What kind of oil should I use? Can I use synthetic? Do I need friction additive/modifier?
A: A quality petroleum/mineral based oil works best in the Detroit Locker units.
We do not recommend synthetic oil. Friction additive/modifier is not required.