Its been a while since ive wrenched on an aw4 equiped xj, but IIRC, theres a butthole chamber in the back of the aw4 housing, that seals onto the imput shaft of the t/case. Some fluid lives here, just enough to spill all over the place when pulling the trans...
I could be confusing the ax15/aw4, whenever i pull drive shafts or t/cases, if i grab a pan, it doesnt leak... If i dont grab a pan, it dumps....