2007 Ford mustang GT rear diff leak

I have a 07 mustang GT with a leaking rear differential and don't know why it's leaking my uncle says there's a vent at the top that is leaking but I think it needs a new gasket why would it be leaking anyone know?

Forgive me if I don't exactly know the layout of your car. Have you added any aftermarket accessories? When I installed Ar Headers to my Camaro, the exhaust pipes leaked a lot for awhile, even a bit further in. I also found that superchargers tend to have a similar consequence for awhile. Like I said, I'm not exactly sure where the problem is occurring on your car and am not familiar with the 2007 mustang layout.

There's a vent at the top, so it's possible that it could be full of water. Have the rear cover removed ( old diff oil STINKS! ), & if everything looks okay, put a new gasket on it & fill it back up with new oil. Also, I think that All Mustangs get a factory posi differential, & they might require some special oil additive.

How would we know? You're the one that can put the car in the air and actually inspect your rear diff to see if it's leaking from a vent, or from a gasket. So, get it back up in the air, get some cleaner, get a flashlight and GO LOOK.