You stated the differential is working properly but has a leak. You could save yourself a LOT of money by doing the following:
Where exactly is it leaking from? First, check the level of the differential. It should be just below the fill plug, no higher.
If the seals are bad they could cause s leak from one or both ends of the axle housings perhaps dripping from area of the brake backing plates.
If the leak is in the center, under the "banjo" it could be a loose fill or drain plug or it could be the bolts around the sides or front of the banjo which should be torqued to 35 foot pounds.
Those bolts have a special thread pitch and should not be tapped as that could cause the bolts to leak.
I have successfully used a product (click on link below) that is designed to seal leaks from the outside by applying the material to the leaking seam or bolt head. The surface must be clean of any traces of oil or moisture before applying.
Of course if the seals are the problem, the sealant is not a solution.
Good luck.
http://www.permatex.com/products-2/p...-repair-detail