This is where it's nice to have a "Chassis Ear" kit.
I ought to get one of those. I can see where they'd be expensive, though, especially with the "wireless monitoring" portion of it. Makes me wonder why someone hasn't taken a small audio recorder and rigged it up to a 'scope. Use a magnet to stick it to the body and the part you want to listen to, drive, then pull it and listen.'
How dark was the fluid that came out? Did you drain it into a clean catch pan and save it? If you put about 1/2" in a small cup (solo cup) is it still transparent or is it completely opaque?
It was grey, opaque unless I was looking at a very thin puddle of it. Even then, the "sparkles" were distributed throughout. It looked like somebody dumped a bunch of really small glitter into NeverSeize.
Unfortunately, I didn't have the foresight to save the fluid in a clean container; I assume that having it analyzed would the purpose, and it'd be worth the cost of the analyzing. Nope, I drained it into the pan I usually use for motor oil. There's always a little of the oil left over after I swap it into a recycling container, so the gear oil is contaminated. Whether it'd make a difference or not in the analyzing, I don't know, considering that I'd be concerned with the amount of metal content in the sample.
I did save the oil in the pan (haven't dug out an old oil container yet to transfer it into), so I just ran out to the garage and took a second look, scooping out the mixture into a clear plastic cup. I can make out the old motor oil (there's not much) and the rest of it is grey. Anything more than a 1/8" thick in the cup is opaque.
I noticed you said the sound clip was amplified, but was the whole clip amplified or did you pick out just that frequency range? Some noise from the R&P is considered normal, and the fluid (if not completely dark with metal flakes) could have just been overdue for a change.
If the R&P are worn excessively the new fluid will probably look nearly the same as what just came out of it in a few thousand miles.
I amplified the whole clip, without picking out any frequencies. The only reason I did that: the original clip required that I turn up the speakers and the computer's volumes to high to hear it. It's definitely not normal gearing sounds. At the ends of the speed range (about 30-32 MPH on the low side; 42-45 MPH on the high), it's pretty hard to hear and the engine noise covers it pretty well. At 35-37 MPH, normal speed for cruising around town, it's definite and loud. The engine noise doesn't come close to covering it up. I suppose I could with the radio; I'd have to be *cranking* it to do so.
I've seen dark gear oil before; I haven't seen it with this amount of "glitter". I don't remember using anything with the limited slip additive in it, though, so I'm left not knowing if the glitter is metal or LSA. If I had had half a brain, I would've drained it into a clean container for analyzing.
I'm okay with simply replacing the differential. Again, worst case scenario, I replace the differential, it makes no change in the symptoms, and I go chasing down another problem. I've gained experience swapping the diff, and I've got a spare laying around the garage in case it does die some day down the road. I've spent more on less educational endeavours :-p.
I believe the NA manual Bajas had a final drive ratio of 4.11 (feel free to correct me if I'm wrong; I pulled it off of NASIOC's forums and didn't remove the diff cover to count teeth). I also believe that the '00-'04 manual transmission Outbacks had a FD of 4.11, too. Seein' as the Baja's allegedly built on the Outback platform, it makes sense to me. So I've just got to hunt down a 00'-'04 OBW, preferably with a little amount of underbody rust and low mileage; maybe something that was totalled due to front end damage or the like.
If I want VLSD, I'd better be looking at an OBW that either had it as an option (good luck finding that info in a parts yard), or one that had the whole cold weather package (heated seats, mirrors, block heater). I'll also keep in mind what 1 Lucky Texan mentioned about the viscous fluid in the VLSD not performing up to task at high mileages. There's the clutch LSDs out there, too, but I haven't done much research in that area yet.