Another approach to axle housing venting is to put a tubing nipple into the housing and run a piece of rubber tubing up inside a frame rail. This will prevent water getting into the housing if the rear end gets submerged at a boat ramp, deep puddle, etc. The top hat type vent will siphon water into the housing if a hot rear end encounters deep water after a highway run. I've seen it happen repeatedly when some of my bass fisherman customers launched their boats after a long run at highway speed. Water and rear end lube does not play well together!
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!