Yeah, I know for a fact that he's talking about the pinion seal because mine used to seep a little bit too. I didn't have to change mine though, I took out the fill plug and drained all the extra oil out of the housing. I think mine had about 8 extra ounces of fluid in there. After I did that, mine stopped seeping. I really don't have a good explanation for why it stopped, but it could be that with more air in the housing, you don't see as high of pressures when it warms up. I didn't see a vent tube when I looked.
As for replacing the pinion seal, I would recommend looking through a ford manual. This is what mine says:
You'll "need" a 2 jaw puller, a companion flange holder, an oil seal remover, and a pinion seal replacer.
1 - Mark (index) and remove driveshaft from front diff. Do not allow shaft to hang unsupported!
2 - Measure pinion preload and record measurment.
3 - Index flange to pinion stem and remove the nut.
4 - Remove pinion flange using 2 jaw puller and inspect. Replace as necessary.
5 - Remove seal using special hard to find puller or big screwdriver or prybar, etc.
6 - Remove oil slinger (big flat washer) and pinion bearing.
7 - Remove and discard collapsible spacer
8 - Inspect all parts, replace as required, etc, etc
9 - Install new collapsible spacer, original pinion bearing, and oil slinger.
10 - Lube pinion seal with 80W90 and install using "special" driver.
11 - Lube pinion splines, line up your marks, and install pinion flange. "Never use a metal hammer to install a tight fitting flange. Use plastic if required."
12 - Install new nut handtight. Use flange holder to hold flange while tightening pinion nut. Rotate occasionally to ensure pinion bearings are seating correctly. Take frequent preload measurements with torque wrench. Final reading should be 5 in*lbs higher than initial reading taken during removal.
13 - Align index marks on front driveshaft. Torque spec on "univeral joint spider retainer bolt" is 14 ft*lbs.
This was all taken from a 2003 Ranger Ford Service Manual. I just looked on eBay and found one listed for 39.95 as a buy it now. Item number is 190139175862. You should go buy it now!!! I spent around $70 for mine.
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