This is really dependent on what shape the gears are in and what ratio they are.
I would pull the diff cover and drain the contaminated oil out.
At that point you can assess if the gears are still OK. If they are you have the option to change the pinion bearing and seal.
If they are shot, your best bet is probably swapping the entire axle.
Depending on tour gear ratio you may be able to find another axle from a xj which would be easier to find used.
Sent from my phone where correct grammar is difficult.
95' XJ Country - Stock Skids - D30/D35 Limited Slip - 3" Lift - 31x10.50R15 - 4.0 HO - AX15 - NP231
98' XJ Classic - D30/C8.25 - 4.5" RC Lift - 33x12.50R15 - 4.0 HO - AW4 - NP231
Originally Posted by Azzy
You can tell the character of a person in how they treat someone who can do nothing for them.