Sorry if this has been asked before, but here goes.
I plan to change my rear diff oil to Mobil One 75W/90 Synthetic. Is a friction modifier additive necessary when using the Mobil One? http://www.dieselplace.com/forum/images/smilies/confused.gif

nope

:badidea: what he said

echerbst & 9W3-HD, Thank you for the reply................