Transfer Case
WARNING: This page is about a different car, the 1988 Jeep Wrangler, 1988 Jeep Wagoneer, 1988 Jeep Grand Wagoneer, 1988 Jeep Comanche, and 1988 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 until it is.