The main seal to worry about is in the housing.
The seal that is in the retainer is only replaced when the bearings are replaced. So in your case replace it. But be sure to replace the inner seal that is in the axle housing. This is the one that keeps the rear end lube out of the bearing and brake area. Make sure to pack the bearings with a good wheel bearing lube. this is the only lubrication that they get. Check this out for reinstallation: http://www.moparts.org/Tech/Archive/axle/12.html