Originally Posted by
afonda
forgot to mention ... there was another tag that read.. 75w140 syn only.
which of course is the oil type.... I think it is odd to find it says synthetic only.
I think it's odd that Ford believes the synthetic oil in the diff is good for the life of the diff. (have not seen or looked for that in writing, just what I've heard from several Ford dealers)
Of course, I guess it's all a matter of perspective. The motor oil that comes in the engine would also be good for the life of the engine if you just left it in there. You'd likely just end up with a very short life.