Sounds like you possibly damaged the inner seal or it was installed improperly. It must be driven into the stop in the housing and driven in very straight or it WILL leak. Axle bearings are not lubricated from the rear end lube. The only lubrication that they should be gettin gis from the wheel bearing grease that you packed into the bearings much like the front wheel bearings. If the axle lube is getting past the seal it will wash out the bearing lube and shorten the bearing life and get into the brake area.