I know this is going to sound very strange, but somehow, there is a fluid that is deposited on the underside of the bed and I cannot for the life of me locate where the fluid is coming from. It is thicker than engine oil, fairly clear, and doesn't appear to come from anywhere, even though the streaks of fluid are directly over top of the rear differential. How I found out was the wife noticed a fluid drip(s) on the garage floor after I moved the truck. It's not a brake line as the fluid is much thicker than brake fluid and I have no loss of brake pedal.
Nor, does the truck make any weird noises or clunks. Runs just like a new truck with 104,000 miles.

What am I possibly missing?

Are there any obvious leaks from the differential?

Sent from my Ranger's driver's seat.

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Baby Girl: 2006 White Ranger XL with many memories. R.I.P. 1/26/15

It is probably a rear pinion seal leaking

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1999 Ranger 4.0 and extreme Snap-on tool fetish

X2. The driveshaft has a tendency to fling oil every where when the seal starts leaking.

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So, it's the front differential seal, you think?
I just climbed under the truck... the front differential seal is totally 100% dry, not a speck of fluid or discoloration. BUT.... directly behind it is the differential case obviously. And it is covered in a gooey film of something, as is the bottom of the truck bed, as well as the exhaust pipe that enters the muffler on the passenger side.
That exhaust pipe vertical section appears to have been crusted over, so that leads me to believe that wherever this stuff is coming from, it's been doing it for awhile.
I think my local Ford folks are going to have to help me out with this problem.