After reviewing the design of the transfer case, I'm now thinking the "no Mercon V" and the introduction of TC fluid is entirely marketing BS. I can not see anything in the TC that would require a "unique" fluid. Or that would be incompatible with a different fluid.
It's just roller bearings and a chain. No clutches, temperature extremes, tight bearing clearances, hypoid gears, etc. Any lightish lubricating oil should be adequate. Heck, even gear oil would probably be fine - at some cost to mpg due to drag.
Anybody see something I'm missing?
There is a dual cone synchronizing clutch on the front drive-shaft gears. It is what spins up the front drive shaft before the actual gears can mesh.
Beyond that, you are probably right. Thing is, for some reason in 2008 they decided to switch to the Motorcraft Transfer Case fluid. Did they change something? I don't know. Is it worth the price of three quarts of fluid to find out?