Non serviceable. You have to change it, technically. My dad was cheap, and he showed me how to pull the seal off, grease it, and glue the seal back on with super glue. Not worth it in my opinion though.
I just had to replace one of my hubs. You can get the hub for $50 from mustangs unlimited. You will need a 36MM socket to get the nut off to remove the hub and it takes 250Lbs to torque it down properly