I agree with Lifemember, if you have 1 of 4 leaking, there could be a problem. The bearings could be going bad, out of adjustment(either too tight or too loose), something faulty in the brakes, or tootight on the adjustment.
I would pull that hub and drum off, closely clean and inspect the bearings and seal, also the brakes to make sure everything is the way it should be. Then repack and reassemble and properly adjust the brakes and bearings.
03 Silverado cclb 3500 drw, D/A, Reese 22k hitch
07 Alfa SeeYa Gold 30RL,2 slides,power everything