Looking at some pictures I have when I rebuilt my brakes, It appears that you could possibly replace the outer seal without removing the brake assembly. Drill a couple holes through the seal and use sheet metal screws to pry it out. I have little slide hammers with replaceable screw tips for this purpose.
But this begs a question... Are the outer seals bad? Are they leaking grease? If they are, and the grease is a bit runny, that would indicate that the inner seals are bad and the gear oil has contaminated, and diluted, the grease in the bearings.