Decided to change the rear diff oil in my F250. I have the Sterling 10.5 rear end which calls for 75W140 and friction modifier. The owners manual calls for 8 ounces of Ford-C8AZ-19B546-A, which is now the XL-3 friction modifier, for those with Traction-Lok axles, such as my truck. My question is, should I put in all 8 ounces, or only try 4 ounces as some have suggested? I also called a reputable shop in Missouri, Custom Differential, and they recommended 8 ounces. Ill be using Amsoil Severe Gear 75W140, and some have said that no friction modifier is needed with the Amsoil. whats the best route to take?