Yes. You should service it. Even if it is not leaking, it is a good general preventive maintenance item. I do mine every 25-30k miles.

There are two different fluids housed in the rear differential housing. There is the AOC (Active On-demand Coupling) fluid which is the "Haldex" fluid that engages the rear differential on-demand. Then there is the gear oil which actually lubricates the gears and bearings in the differential. You need to figure out which one is leaking first. Given the spray pattern, it looks like it could be the input prop shaft seal leaking, which might mean it is gear oil and not AOC fluid you are seeing. You should be able to tell by the smell (if you know what gear oil smells like then you know what I'm saying).

Either one leaking is not good.

 

Is it worth it to service both? I’ve only owned the car for 5k miles so I have no idea if the Haldex has been serviced (car has 122k miles) I’m also getting some drivetrain whine, is there a chance it’s related to the diff being potentially low on fluid? Thanks

 

Once again, YES. Fluid is cheap compared to parts. If you don't know the service history, I would always recommend a full Stage Zero fluid service so you know where you are starting from.

If the diff is whining, then it is likely that some damage is already done. I would start by draining the gear oil in the rear diff and inspecting for metal glitter. If it has metal contamination, start searching for a new (or used) rear diff. If the fluid looks clean, proceed with a full fluid service (gear oil, and AOC fluid/filter). Be sure to find the source of the leak and fix it.

If you do all that and still have the whine, I would look at the front bevel/angle gear. In fact, you should replace the bevel gear oil on the same service interval as the rear diff anyways.



Here is what I would recommend for drivetrain fluid services.

Transmission fluid - 3x drain and fill every 30-50k miles, depending on climate and driving conditions, More heat and more stop and go traffic = more frequent changes.

AOC Fluid - every 25-30k miles. It gets dirty surprisingly quick.

Gear oil (front bevel and rear diff) - every 50k miles. This one is probably the least important as long as there are no leaks.

 

i have the fluid on the way to do the front angle gear since its pretty easy, ill be on the lookout metal in the old fluid. I did one transmission drain and fill where i removed about 3.5 quarts of fluid and added back the same exact amount, also did a TCM reset. Ill definitely do the rear diff first just to eliminate the possibility of that being the issue, then ill proceed with the haldex service. I hadnt considered the possibility that it was the diff that was leaking. Thanks!

 

If you do see metal glitter in either fluid, are you going to spend $2500 for a new AOC or $4000 for a new diff, this is just for parts no labor.
Or just top off the fluid and not worry about it. As mentioned, it does look like the AOC input shaft seal.
fcpeuro.com does have a fluid change kit, new AOC pump kit or a new pump filter/fluid kit.
Older models require driveshaft and AOC flange removal, newer models do not when removing/replacing the AOC pump and/or filter.
Xemodex.com is great source for Volvo and other car module repair/info. Xemodex repair info does not apply to your issue, it is a great site to review for information.
PDF directions for AOC front seal replacement.
Differential Electronic Module with Pump Package Repair for Volvo | XeMODeX Inc.
Volvo S60 Parts | FCP Euro

 

apologies for the late reply. ive heard both the diff axle seal and the AOC axle seal could be the cause of the leak, although i assume there isnt a diff axle seal because the driveshaft goes into the haldex then straight into the diff without an axle. from what ive been able to gather you need to remove the driveshaft and use something like a windshield wiper puller to pull out the seal and press in the new one with the correct size pipe/tube. the documents you sent call for a number of special tools that im sure are very expensive, are those 100% necessary, or will i be able to do the seal with what I already have? Also, for the fluid in the axle/diff, should i use liquimoly gl5 75w-90 gear oil, or volvo transmission oil. Ive seen both used and the liquimoly seems to be significantly cheaper and possibly better according to one video. Thanks!