I only noticed the oil leak when I shifted into 4WD and heard a growling noise from the Transfer Case. I went back into 2WD until I could get back to a parts-place (this was ontop of a snowpacked Loveland Pass). I thought I might have trashed the transfer-case but 1000miles later it was doing fine (but the new seal was still leaking). Replaced the endhousing, bushing and another seal and it starts howling.... It does sound too coincidental.
The next step is either to swap in a rebuilt transfer case or, I was thinking, replace the outer bearing. It does look like the seal may be leaking again too...