So, did a rear diff service on my new-to-me 99 XJ today, is only 2WD and has a Chry 8.25 rear. Old cover was siliconed in place and a challenge to remove but I got it off eventually. Worst part was removing the bolts. I'd swear previous owner put them on with an impact gun. They were impossible to remove, had to use a breaker bar to loosen all of them, 12 point socket stripped the hell out of a couple bolt heads, had to use 6 point and even that distorted the bolt heads. Ended up at Ace Hardware looking for new bolts, 5/16 x 18 and 5/8 inch long with flange head. Was impossible to find. Ended up with flanged head bolts the right size but 3/4 inch long (and grade 8) and ended up cutting them down to correct length. Everything cleaned up nice, primed and painted the cover (satin black, nothing fancy), Fel-Pro gasket with a light schmeer of Ultra Black on both sides and bolted it all back up, new bolts worked great. Waited 2 hours for the rtv to set up a little and filled with Amsoil Severe Gear 75w140.

So, if you're thinking about trying it yourself and need diff bolts: 5/16 x 18 x 5/8 inch long, with flange head.

 

I've never known of a diff where an extra 1/8" of bolt would bottom out. They usually come out with more than that length of old sealants attached.

 

i thought there"d be enough room for the additional length too, but i ran the longer bolt in a couple of the holes until it bottomed out and there was still a gap between the flange head and the face of the diff. The gap was narrow, probably less than the thickness of the cover (though i didnt measure it) but it was enough to concern me, so i chucked the longer bolts in my vise and cut them down to same length as stock, just to be safe.