Leaking front axle?

I've got a friend with a 2000 Ranger 4X4. She said something was leaking and asked me to look at it. I thought it was just an oil leak at first (just a few drops on the pavement) until I got under the truck. The engine and oil pan are relatively clean and show no signs of leaking oil. The front right axle, however, is covered in grease/oil/sludge. I don't know much about axles, so my question is this: Can an axle leak? If so, is it difficult and/or expensive to fix?

I'm just trying to help her out and avoid her spending too much at a crooked repair shop. Any help is greatly appreciated.

well. it would be best to start checking things. you can check rubber cover on cv joint on each end of drive shaft. the if the cover is not ripped then remove fill plug on front differential and it should be right to top of hole.starting by cleaning everything is best bet.it could be leaking around seal where drive shaft goes into differential. lots of things to check if you want to save money.