ok I have an 04 F150 5.4. Anyway drove truck about 200 miles this weekend. When I got back home, unloaded truck, noticed a fluid leak on the ground in the rear of truck. Upon further inspection, appears to be leaking from where the driveshaft meets the rear axle...looks like there's a gasket or yoke in the rear of the U joint? a little fluid dripped down and ran down to the lower portion of the "pumpkin" and made a quarter size oil patch in front of my house.

I would have definitely noticed such a stain before, since I park in the same spot at home and work every day. I drove to work today (14 miles) and looked under the truck for 15 minutes after I parked, don't see any drip, but do see remnants of a leak all over the front part of the rear axle. No way has any fluid leaked on the ground before, I 100% would have noticed a stain.

Thoughts on a fix for this? I had the clutch packs redone about 3 years ago under warrannty, truck has 88k miles. No shudder when I drive from the rear axle, I'm assuming there is fluid in the rear gears, as a substantial leak I for sure would have seen on the ground. leak is 100% NOT coming from the seal on the rear axle, but in front of it where the shaft meets the axle. Possible that driving on the highway at 75MPH for 2 hours straight caused this leak, as my drive to work is mostly stop and go, both ways.

I know it has to be fixed, just trying to figure out costs..

 

Sounds like a pinion bearing or pinion seal going/gone bad

 

If it happens only when you drive long distances and only when you get the differential warm. I would suspect 1 of 2 things.
1st check your vent tube that runs from your axle up to the frame for blockage or restrictions if it is plugged up by mud or a leaf cutter bee the axle will build up pressure and it will eventually come out of a seal somewhere.
2nd maybe your pinion seal has started leaking and it's only bad enough to be noticed when it is warm.

 

I have seen this a few times at my days at "Mr.Lube". The vents just get clogged and pressure builds.