There should be a small piece of tubing threaded into the top of one of the axle tubes with a wobbly dust cap on top to keep dirt and varmints out. It allows the axle housing to relieve air pressure as things inside heat up. Sometimes they get clogged and internal pressure forces the lube past seals and gaskets. Sometimes the bolt holding the brass brake line junction block on is center-drilled to also be the housing vent.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!