Over 90% of issues with transfer cases are caused by low fluid. With some transfer cases hold a quart of fluid or less. So virtually any leak is a major cause of concern. When any fluid spots are under your car, it’s imperative that it be checked out immediately. Very seldom do these units “wear out” the vast majority are low fluid levels. Once the fluid level is too low, it will wear forks because they are made of plastic, and need to be constantly cooled by the fluid. More and more contain clutch plates in them, these clutch plates have paper friction material and easily burn if not kept cool by the fluid.
These pictures are of a transfer case fork damaged because of no fluid, and a brand new replacement fork. The plastic fork pads destroyed and the hub needing replacement as well. Cost of these 2 parts. ~ $450 plus labor