I have an 03 F150 4x4 and the rear is leaking by the driver side brake rotor. Could it just be a seal or more serious? And how much does a seal cost to get put on? Dont really wanna try it myself since I have never done it. Thanks for any help

 

Axle seal leak seals 15-20 bucks will also have to have rear diff fluid and silicone. Remove rear diff cover and allow to drain pull wheel and brake caliper and rotor. Pull the c clip retainer bolt and pin slide out axle remove and replace seal. Reverse tear down fill with fluid

 

I would change passenger side seal also while it's already opened up.
also check bearings.

 

Also inspect the axle shaft itself for pitting or wear in return caused by a bad bearing. Mine was just spraying the fluid!