I had the same problem, and I had hoped it would just be the seal that needed to be replaced. So I took the driveline apart, and pulled the yoke, and found a slight rut worn in the shaft of the yoke. Some little piece of who knows what got in between the seal and the shaft, resulting in the small rut. It was leaking pretty good. New yoke was about $145, and the seal was $45.
If you do this yourself, you'll need some special equipment, including a large slide-hammer type yoke puller, a 3/4" drive impact gun, and a 3/4" drive torque wrench, not to mention a 1 7/8" socket.
If you take it to the dealer, count on paying for about an hour of labor, plus parts.