Carrier/rack problems of the 2008 Mazda CX9

My wife was driving the kids and all of the sudden the car started to make loud noise could not move forward and forced her to stop. Next day we towed to the mechanic's and was told the differential was cracked and it has been several cases of this happening to this car. A week after getting that fixed, I still hear notices when I am driving below 30mils. Now the mechanics tells me the back axle is leaking oil right next to the back differential. This needs to be investigated before a lose of life. If my wife was driving in a highway, there would have been a major accident.