Ford is the only car dealers that I know of that still offer that posi additive
Do NOT use synthetic gear oil with any clutch type posi unit
I had a customer, a real good lawyer, that I help set up a 8 3/4 3rd member with a new clutch type posi and 3.23 OEM Mopar gears that he had a local shop install in the housing and they use synthetic gear oil with no additive, which ended up making the posi unit try to lock up going around a corner which almost made him crash That shop ended up swapping it out for a different style posi that uses gears instead of clutches and charge him double what I had sold that other unit to him for