My first thought is axle seals...left rear rim, on the inside rim is caked with grease, Had a anothier flat, and as I was putting the spare under the box, I observed this on the 04 F-150, the bottom of the hub is wet with grease as well, look's like this has been going on for a while, I did not pull off the left rear tire to check....

 

I'm not sure if it is the seal or the way it was installed, but I've seen quite a few leaks from there axle seals. Check your brake pads/shoes to make sure they are not oil soaked. If they are it is a good idea to replace them, the bad thing is they come in pairs.

 

I pulled off the rim, booth pad's and rotor are ok ( groved but ok, not going back for a 2nd turn of the rotors ) on the axle shaft it is leaking quite badly, not grease but diff Fluid..

I topped of the fluid level in the diff, it was down a bit, Once my othier truck is built, I will advise the dodge dealer that Ford needs to fix this. Until than, if the 04 F-150 ( just shy of 40,000 Km ) breaks, she breaks.

 

this totaly sucks, Booth seals are now leaking ( 04 F-150 ) and I will have to rent a truck or take time off work to get the F-150 under the knife, Yes this is a Pro Ford site and I will be happy happy happy when this truck is some one else's headache, She's leaking good, booth rims are kicking gear oil up inside the rear fenders, my tires are coverd in this crap and it stinks, all the othier Ford guys at work are asking me what in the hell have I done to this truck, they can not beleave Ford builds this level of goodness into a pick up.

Any way check your axle seals and bless your Ford, or kick it ( kicking did not work for me ) Keeping up the fluid in the diff is geting expensive, I blew one rear end in a 02 F-150..

Just needed to vent, looking forward to life on the dark ( dodge ) side, off to watch the Flames vers duckies, Good luck to all who worship the blue oval....

 

Today, Saterday Ford dealer replaced booth axle seals and booth rear pad's and turned the rear rotors due to all the diff fluid all over every thing...Next time your under your truck check it rear rotors, service tech advised me this is the Fourth F-150 he has seen this month with leaking axel seals aug 03 was my build date...

Truck was pulling right hand turns all buy it self when breaking due to the leaky seals...