Hey B,
Its actually the seal between tranny and t-case. My rear main engine seal is just sweating, like every other 4L on the planet.
I changed it about a month ago, and hadn't had any puking before. but of course, i swapped the fluids to synthetic. When I filled it, i made sure that the fluid was below the fill hole. I'll crawl underneath and check to see/feel if its wet near the vent.
Thanks !