I'm guessing that you ned to pull the axle trumpet, as you might as well replace the oil seal(s) while you are in there. Old style has 1 seal.. new style has 2 seals. Axles aren't interchangeable.. so you need to know the year of your tractor, which can be found via serial number.
the N board over at ytmag.com has tons of N-formation on topics just like this.
Soundguy