Rear Differential repair on 1998 Ford Expedition

I heard a loud rumble from the rear end and had a diagnostic which stated there is a problem with the rear differential and its leaking oil. Does this mean it needs to be replaced and how costly is this type of repair?

1 answer
the noise is the problem. that could be a bearing or ring and pinion. yes, it is costly. overhauls are around 900-1300 depending on needed parts.

Roy