Ok want to change my fluids in my differential's (99 k1500 suburban) the owner's manual says that if it a locking differential that it does not need the additive , but the dealership's and auto stores says it does need it. Whould it hurt to add it are should i leave it out. Im kinda confused on who is right owners manual are every one else that i spoke to? im kinda leaning to every one else.
tia