A leaking seal can be like a canary in a mine warning of other trouble. Be sure and examine the axle and bearings for wear and slop. If there is a worn groove on the axle where the seal rides, a speed sleeve may work to provide a better seal surface. Another thing to check is the fluid level in the differential, and the functionality of the axle vent which releaves pressure when fluid warms up. If that is plugged fluid will be forced out through the seals. I've usually replaced seals and bearings at the same time, I just don't like going back....
