Just took my 1996 XJ in for a new harmonic balancer replacement, as the seal behind it was worn out and the balancer was "wobbly"! This happened after a 4000 out of state trip I recently did. I ordered a new balancer and the dealer said it doesn't come with a oil slinger. And the shop I took it to didn't replace the oil slinger after I mentioned if it needed a new one, put it on. Does the 4.0 not need one?? My power steering pump grenade inside when I was on my trip and it was replaced as well as a new idler pulley and serpentine belt, two days after that, I heard squeaking off and on, and it was determined my balancer needed to be replaced after a friend saw it running/wobbling. My idler pulley looks awfully close to the mount it is on, almost like the mount is bent a bit. But this shop I took it to here where I live didn't see anything drastic. Hard to find a decent repair shop where the techs know what is going on and they are detailed pros!!@#$Q

 

Replacing the oil slinger requires removing the timing cover, and not something you'd need to replace when doing the harmonic balancer or the front seal. It's possible the new belt was installed too tight, or even to the proper tension versus the old one being too loose and that put the harmonic balancer over the edge and start to seperate. It's not a bad seal that makes it wobble, its the balancer itself separating in the middle where you see the rubber. It's just good practice to replace the seal behind it while replacing the balancer, although just as often the seal leaks and people replace the balancer along with the seal.

Hold a long straightedge across the face of the idler pulley and see if it's really crooked compared to the belt. A new pulley should be pretty straight, whereas a bent mount or worn out bearing will be noticeably crooked.