Hi.
. I bought a 2000 Ranger in the summer. It has a rear main seal leak that does not get on the ground but at high speeds leaks onto exhaust. The previous owner said he replaced it when I purchased the truck. Assuming he told the truth what could be the reason that the new seal leaks? Is it possible to install improperly? Blue Devil stopped the leak quickly but only lasted about 500 miles.

 

It's probably not the rear main seal but the cam shaft end cap, it's a common "leak" problem for the Vulcan.
That would explain why the Blue Devil sealed it. It's very unlikely a stop leak product of any kind would seal a crank shaft leak given the fact that the crank is always moving.
The other place is the pan seal.

If you get in there use a Ford crank seal as well as a Ford cam seal, don't use aftermarket parts here.
Use a good quality sealant on the cam seal, just don't install it dry.
Drive the crank seal all the way home, not flush with the block.

I have to do mine again, from experience, I'm going to pull the engine rather then dropping the trans.
I plan on mounting the engine on a stand, so much easier then crawling around on the floor in that tiny space.

 

I guess I should take a PIC. The leak is right on the bottom before the pan. You can see oil beads there. There are no leaks on the or around the pan. I did more Blue Devil. Fixed it right away for 4 days. Today started leaking again. I am unfamiliar with the cam seal. Where is it located? Is it involved to replace it? I want you to be right but it seems like the seal is messed up because the oil beads are all around the bottom of trans. It seems to be leaking where the back of the trans bolts up just before the oil pan. It's not trans fluid. All along that seam is where the oil is beading up. Guy said he replaced that seal recently. But I assume the rear main seal is there. Would the cam seal cause oil to be there?

 

Yes, the cam seal makes it look like the rear main seal is leaking.
The cam seal is above the crank seal in the centre, so any oil from the cam seal will collect in the same place.

 

Thanks. Any idea what a shop charges? It may be more than I can do. I have never removed and engine or dropped a trans. I have no hoist for engine.