Carrier bearings support the differential case. They sit on both sides of the ring gear housing. These bearings keep the differential aligned. They must withstand immense lateral forces as power is sent to the axles. They ensure the ring and pinion gears mesh perfectly.
Low fluid or water entry will ruin carrier bearings. They will begin to pitting and make a roaring noise. If left unfixed, the differential case will wobble, chipping gear teeth and locking up the rear axle.