I went through this drill with my '55 first series. This axle assembly has some "c" clips in the differential housing that will need to be removed. You will not be able to remove the axles until those are off. Then the axles will come out easy, at least mine did. I recommend either a factory shop manual or Motors Chiltons to get the steps right.
I think the reason my seals failed was due to the axle vent being plugged so there was no relief when the fluid warmed up. The only place it could go was out the seals. My truck had the open Hotchkiss differential, but if you have a torque tube and have been topping off your tranny, that fluid may have found a path through the okie bushing and seal back to your rear axle seals.
