Swap them out, the bad T-case is the np249. It's he all wheel drive T-case. any where after 60k miles the Viscopular(sp) locks of and they start scrubbing the front tires. Most people will swap it out for a 242 or a 231, both are bolt in's. Only thing you need to change is the front drive shaft there are 3 different lengths. And yes the XJ front shafts can be used..
I found the drive shaft problem out the hard way. Swapped a 231 in and didn't do the drive shaft swap. After a year of bottoming out the drive shaft I have toasted my front axle.