Automotive Forums

We just bought a 2006 Expedition Limited. I noticed just a spot of what looked like some kind of oil under the vehicle. After inspection, I found that it was coming from what looks to be a coupling in the passenger side front axle. The axle comes out of the transfer case, into this coupling (not sure if that's what it's called, but it's two round flat metal pieces bolted together), and then there's a boot and then on to the wheel. When I looked at the drivers side, that coupling is wet, too. I am wondering if there is something wrong or if this is normal, considering it is that way on both sides. I am hoping this is something that gets lubed and is just overflow or something. Can anyone help?