Transfer Case
WARNING: This page is about a different car, the 1989 Jeep Wrangler, 1989 Jeep Wagoneer, 1989 Jeep Grand Wagoneer, 1989 Jeep Comanche, and 1989 Jeep Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
Remove fill plug. Check oil level. If level is not up to fill plug opening, add lubricant.