'98 suburban front diff. vent leaks oil

in my front differential out of no where my vent valve starts spewing oil out and my 4WD isn't even engaged i have no clue why it is doing it?

also has anyone here heard of a dodge no leak vent valve

The only thing I can think of its it's severely overfilled. As the brakes heat up the fluid, it expands, and comes out the vent