EDIT: Though it could depend if you talking about grease or an oily greasy mixture on the balls since that means you need to replace the inner axle seals / rebuild front end.
If its just grease the wiper seals are designed to let some out over time to keep the balls shiny and clean. Maybe its overfilled alot with grease.
Also open up the fill/inspection plug on the front diff and see what the condition of the oil is if its goopy and thick the seals are shot .. if its oily with a slight tinge to none of grease then it might be ok yet.
Proceed with calculated steps and avoid "MUD-paranoia" there is a wealth of info here and if not careful you can easily spend funds on projects that may or may not need immediate attention, read, acquire knowledge- flame on.....