No, not behind the third...sorry to confuse you.
Theres one that's more of a dust seal that gets installed before you press together the axle/backing plate assy., and one that is in the end of the housing. The one in the end of the housing is the "inner" seal, as the other one is in the bearing retainer the goes in the backing plate, more to the "outer" side of things.
Its right there in the end of the axle housing- you'll see it easily when you pull the backing plate/axle assy. out.
Ryan
