That's nothing more than a leaky pinion seal that is both inexpensive and relatively easily replaced. If you're not handy with tools, any 4x4 shop or mechanic can easily replace it. It takes about an hour and the part is under $20. If you want to do it yourself, a very durable brand of replacement seal is Chicago Rawhide.
A forum community dedicated to Jeep Wrangler owners and enthusiasts. Come join the discussion about reviews, performance, trail riding, gear, suspension, tires, classifieds, troubleshooting, maintenance, for all JL, JT, JK, TJ, YJ, and CJ models!