After the first big snowfall i noticed while my '04 2500HD is in 4 wheel high under acceleration i can smell gear lube while the heater is on. It hasent left any puddles i can see but it has been snowing like crazy out so its hard to see. Anyone else notice this ever? Any idea what might be going on? Im thinking a vent hose routed wrong?

I also noticed this. I have the front differential filled with synthetic, but still have the old non-synthetic compatible breather. I thought that may be why I was smelling it....?

Rear axle seal leaking ??

Only does it in 4 wheel drive under acceleration. Never in 2wd.

My breather cap on the diff has worked itself loose before. The fluid then makes its way back to the rear of the truck at highway speed. Lots of hot places to smoke on.

04d-max

With my 2000, fluid would work its way up the vent tube and out the vent cap.
It was nasty, gear lube would drip down on the drivers side upper arm. Got all
over everything. Only did this when in 4 wheel. I took some fluid out of the
front diff, about 1 cup, and problem was solved. Find the vent cap and see if any lube is leaking out. Hope this helps, good luck.