If as we assume talking about the dust flange behind the rear pinion flange you could very easily fix that without removing it. Just hold in place and hit the pinion/flange join with a quick tack with a arc welder. Just a couple of very small tacks on each side will hold and doing it quickly will not create enough heat on the pinion to damage the seal or start a fire. You don't need much to hold it as it is not a loaded joint.