Possible bad axle

I came across a deal too hard to pass up. A loaded 2000 XJ for $900 thinking i could make a few quick fixes. Got it on the intrerstate and it is extremely loud, coming from the rear axle. I have a very limited amount of mechanical knowledge. I was going to take off the rear driveshaft and replace the u-joints on it to see if that helpes any. I then sheared off 3 of the 4 bolts holding the straps and of course the shaft ended up breaking free from the last strap. I plan on taking off the diff tomorrow but what besides metal shavings or obvious signs of damage do i need to look for before i replace the axle? As you can see, the yoke has been leaking. The front axle yoke also leaks, trasmisson light is also on. Part time light stays on all the time tll even though it doesnt feel like it is in 4wd all the time. Like i said 2000 xj transfer case has full time 4wd, dana 35/30 from what i can tell, roughly 175k. From Ohio so there is some rust. Probably not been maintained well in recent times.

Sent from my SM-G920P using Tapatalk

From your pictures it looks like a 8.25 to me. The flat flange on the bottom is the tell tale sign. Dana axles do not have this.

There are a lot of good 8.25 axles out there but there are a lot of bad ones. Pinion bearings frequently go and carrier bearings can go as well. With bad pinion bearings acceleration and deceleration can affect the noise whereas with carrier bearings its usually an audible drone at all speeds over about 20 MPH. If it was very loud I would expect to see liquid metal come out. Given how common stock axles the aren't worth fixing.

Don't replace expensive stuff without a diagnosis, even if you have to pay somebody with experience a few bucks to look and/or listen to the symptoms. Fresh u-joints are a logical and inexpensive way to start both diagnostics, and catching up on the maintenance.

I concur, dont start expecting the worst right away. If you are not proficient at setting up a set of gears or changing out those bearings (if necessary), please take it to a gear shop and have them give it a good go-through. Obviously at this point you will have to tow it there, but it shouldnt cost more than a Bill and a half to have a competent shop go through it and diagnose the issue(s). At that point you will know what is going on. When they give you an estimate on what the cost of repairs will be, then you can make an educated decision on whether to have that differential repaired, get a replacement differential from a boneyard and install it, or upgrade to a beefier differential if you feel you absolutely need it in accordance with what you plan to do with your Jeep. Hope this helps to direct you in the right direction, good luck!