90 XJ rear end problems

The rearend in my 90 XJ 4x4 sounds about like a rock tumbler. Seems to be coming from the differential. My question are should I have this one rebuilt or is there a newer version that will bolt in? I kind of like the idea of getting disc brakes in the rear as I see on newer models. I'm using stock tires and lift currently but am wanting to get a 6" lift & bigger tires hopefully in the near future. Whats my best bet?

Try this:

http://www.naxja.org/forum/showthread.php?t=47305