Had it on my 05 WK at a fairly low mileage, 38K miles. Rear pinion seal leak. I read the Service manual procedure which detailed complicated use of torque readings via rotating the back axles to get correct yoke/pinion nut tightness along with how to set the new crush washer torque. Too much for me so took it to Dealer who apparently repaired it the way I would have anyway...take off axle/yoke/pinion nut, remove seal, new seal, new crush washer and "snug" it up since the rear wheels were never removed.
You probably got a "wet" looking front side of the rear diff, right..?..not covered in oil, just "wet" looking if your diff. level is low.
If you take a look at the WK Service Manual PDF downloadable for free ( I am assuming you have this model), and you are a DIYer you can get a good idea what is entailed in changing out the seal. You will need to fabricate a holder for the yoke to get the pinion nut off..a piece of steel flat bar with a hole for one of the 4 yoke bolt/nuts and long enough to hit the ground and block further movement as you take off the biggie nut. YouTube has some generic rear pinion seal changeouts which help familiarize you with what is involved. If done at the Dealer here, the cost was around $170-$200..I was still under the Powertrain Warranty. I want to do my own repairs usually since I enjoy it and the local Dealer is a Ford Dealer who inherited the Jeep franchise as an afterthought....their Service Techs have slipped up the 2 times I got them involved with my JGC.
If you need to wait to fix, you can try adding a diff. seal voodoo sealer/additive but you know how good they(don't) work since those sealers really need some heat put into them which the diffs don't really supply.