Transfer case went pee

I have an 83 1/2 ton chev with a warmed over small block, built 700r4, and 32 inch tires on it. It sees a fair amount of time off road, and lots of time in four wheel drive in the winter in alaska. Recently, it started making a really loud noise, constantly, that sounded like the chain. Oh, it's a NP308, also by the way. I crawled under there, and fluid was dripping out of it pretty quickly. Couldn't tell where from, but it wasn't the rear slip yoke. Maybe coming from about half way up the passenger side, but not sure. there doesn't look like there is a crack in it. I guess my question is, do these things break often, and if so, where. Do they have vents that get clogged, and could cause the stuff to leak out when the t case warms up? also, the four wheel drive still works, so I'd rule out total internal failure. Thanks

 

NP208, not 308, typo.

 

My sons 97 K2500 cracked the tailshaft housing and went to leaking badly. Started with a vibration and within a few miles the housing had cracked. Turned out the cause was a frozen U-joint (sealed joint) at the front of the driveshaft which was levering the tailshaft housing as it spun. The resulting cracks were tiny, almost impossible to see without good light.