I just went from 308 to 373 reargears...and i did my break in period so i need to change the gear oil..but my question is the shop added the friction moddifier i gave them with the 2 quarts of royal purple oil.... do i need to add friction modifier with the new oil? reason is it stinks like holy hell and i just dont want my house smelling lie that..so is it really needed???? 
