Transfer Case
WARNING: This page is about a different car, the 1990 Jeep Wrangler, 1990 Jeep Wagoneer, 1990 Jeep Grand Wagoneer, 1990 Jeep Comanche, and 1990 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.