with the rear diff leaking, this is the first that I am hearing about it. If the dealer has already fixed it twice, chances are they did not do it correctly, so I would take it back there to have them redo it. Complain hard!!!!!
As for the brakes. Are you sure that it is just not a squeak that you are hearing instead of the indicators? Our brakes squeak alot unless you break them in or if I remember it is called bed them.
What you have to do is get on a road way that has limited traffic. Get the car up to 60 MPH and hit the brakes hard without engaging the ABS. Bring the speed down to 10 MPH and without stopping. Then accelerate back to 60 MPH quickly and brake again to 10 MPH. Try not to let much time in between the braking so that the pads/rotors stay hot. Do this 6-8 times. When you are done, drive around for 15 minutes or more without braking to allow the rotors to cool nicely. What this does will put a nice coating on the rotors that will improve braking and also keep them quieter.
The bad thing is it can get you in trouble with the police if they are near. I got hit once, but once I explained it to the cop, he was more than happy to let me go.
Mango, the other mod here has been around the Charger longer than me, so maybe he has heard something about the rear diff leak and he can shed some light on it.