I was checking all my brakes and front bearings out before summer started and found my rear brakes to be oiled and gummy, again. First time I thought it was my wheel cylinders, so I replaced them. Well I definatly can smell the gear oil now. I already have seals and bearings so I thought I would just go ahead and replace those. I wanted to know how one may test the axle vent/valve to make sure it is working? This isn't the first time this axle has done this. My brother redid the seals and stuff once before already. I just want to do this right and make sure I won't have to do it again, for a long time at least. Any advice or suggestions, please bring them! Thanks for the help!

58' 3200 235 3-speed/OD