My mechanic has advised me that the output bearing (rear) in my XJ is the cause of some mild vibration and noise. The rear suspension had been altered by the previous owner, but I’ve replaced the leaf springs and shackles to restore the suspension to where it should be, and the noise is hardly ever present. I’ve inspected the transfer case rear output and no leaks are visible. The thing drives really well. The trouble is that it can’t be repaired without opening up the transfer case, which means I may well be better off with a rebuild, and that ain’t cheap. So how long can I procrastinate on getting this repaired? How will I know it’s time to definitely get it done?