^^^ You can't go wrong really. I've got all Royal Purple Synthetic in mine (minus the Friction Modifier of course). After the fact, I've heard Royal Purple Diff oil isn't the best - but I don't remember why. I'll let you know if that's true this coming season - haven't really driven the Mustang since the new diff. oil went in.

Another way to go is to use Redline Gear Oil, as it comes with 5% slip modifier already in it, which should be enough. If you use too much friction modifier, you're basically defeating the purpose of the LSD.

how often should this fluid be changed, mileage or years?

^ I think Ford 75w140 synthetic is good for 7yrs 150,000 km. I wouldn't let it go that long though.

5 yrs and 5000 kilometres is alright?^^^

I would say that after 5 years I'd be changing it even if only 5,000km. If I ever kept a car long enough I would change it every 2 years as well as the trans but that's just me.

^^^ Good tip. Most cars never see the oil changed .... Not good.

^ yep and even with low usage engine oil gets changed in the fall when I park the car and in the spring when I take it out. The most over looked fluids though are brake fluid and coolant.

I will have all the fluids changed out this spring if I still have the car

Had mine all switched over to Mobil 1 full synthetic the day I picked her up:tup