Have you had the diff fluid checked lately? If you haven't I would start checking it until you get the leak fixed, just to be safe.
This is the only pic I could find and I don't know if it look the same on your truck. That would be the vent end and the other end would be attached to your rear end, If you can pull the hose off the rear end and blow through it then. . .duh its not pluged lol.
From the quick search of explorer and ranger sites is seems that changing the axle seals isn't impossible, the seals are cheap and should be in the range of a fairly mechanically inclined person with a mild set of hand tools.
Rear Axle Seal leaking... Thread on Explorer Forums
Hope this helps!