i don't know squat about the Mustang, but i would suggest you at least have the dealer diagnose the issues.
My Z06 leaked diff fluid right after i bought it. two trips to the dealer and a new compression washer later it was cured. i would get a little fluid to blow out the breather at the track but like yours just damp at the vent.
now on the e36 with the change to 3.64 gearing i cooked the diff fluid until i went to the vented cover. is it possible you might need a tranny cooler Rodney? vented diff cover?
_________________
BenchWarmer Motorsports
another one of those damn LeMons heads
just another Chump
we are an Autocross Club Dammit............