Is this what I think it is?

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Sorry apparently uploaded one that was too compressed

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Photo is too grainy for me to tell anything. If it's gear oil then you have a bad axle seal. Replace the axle seal, retainer, and wheel bearing on at least that side, but I would do both sides.

I would check your diff breather as well...

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Diff breather is corroded but not stuck shut. I'm about to do the diff breather extension mod anyway.

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Should be a better photo here. I did smell it and it didn't smell like gear oil from what I remember in my lube tech days but that was GL5 and I know not all gear oil has the smelly additives. It's on the outside of my brake drum a little bit (looking at it through my wheel spokes).

I would say that axle seal is leaking. That's what it looks like.. :-)

Yay >< Here I was thinking none of my needed repairs were too pressing but I guess this one is (pardon the pun lol). Now to find someone with a bearing press and ply them with copious amounts of alcohol lol.

Now to get all the parts together I need the bearing, one spacer (the one that mates with the seal), probably a C clip and the inner and outer seals? Is this one of those times when you really really want to go OEM at least for the seals or do kits like this work as well Low Range Offroad Ultimate Rear Wheel Bearing Kit Wheel Bearing- Toyota 4Runner, T100 & Tacoma (Japanese) Rear Axle Bearing Service Kit with ABS (1990-2000) Kit-1001. Also if I go OEM I want the seals from 01 and 02 4runners and not before because that is when they reworked them correct?

The seal was updated, I don't think they are different if I recall, the bearing is different for 01-02 3rd gen 4R's. You don't technically need to do both seals and both bearings unless the bearing is actually bad which can cause the seal to prematurely wear and leak, seals can leak from age and wear aswell before you decide everything must be changed. Use the recommended tool and press it apart if you change the bearing so you can reuse 1 retainer and the ABS tone ring, measure everything twice before disassembly and put everything back in the same location within +/- 1mm if it hasn't been messed with before. Here is a pic of the best method for measuring it, I've done this job 8 times for locals without issues, never bothered with flipping retainers, just put it all back exactly as you found it. Could be a wheel cylinder aswell, but you would be losing brake fluid, you will also need new brake shoes either way.

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I don't think I'm loosing any brake fluid but to be fair this does seem to be a pretty small slow leak and I did do a bit of a flush the other day on that and didn't pay attention to the reservoir levels. Hopefully it is that as that' something I can tackle much more easily. Either way, brake cylinder or or axle seal, I now know why my ebrake is kinda wimpy and I have to crank the crap out of it lol. Only one side is currently holding my truck it seems.

Little bit more investigation. Got the truck on flat ground and checked the diff fluid level. It's right at the threads, once again I don't know how much fluid has already been lost w/e fluid it is so that might not tell me much although I have a feeling this has been an issue since I bought the truck about a month and a half ago as I noticed the ebrake issue way back then. Rubbed a bunch of the leaked fluid on a shop towel and definitely did not notice that nasty gear oil smell which I did confirm the diff fluid does have. At this point I need to bug my buddy who has a jack and we need to pull off the drum. If the entire inside of the drum is covered in w/e it is though I'm not entirely sure how to determine if it's the brake cylinder or the seal though.

Might be brake fluid then. As it can only be gear grease or brake fluid.

Wheel cylinders can start leaking granted your fluid level would have to be dropping as well.

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Pull the wheel speed sensor from that side and turn the wheel while looking at the tone ring. If the tone ring is wet then it's the inner axle seal leaking and not brake fluid. At a minimum you need a wheel bearing, one retainer, and an inner axle seal. I would recommend buying an extra inner axle seal because you will most likely install it incorrectly the first time. Almost everyone does for some reason. Do a grease test/sharpie test to verify that the inner axle seal is riding in the center of the retainer. I recommend using gear oil rated rtv between the inner axle seal and axle housing and the retainer and axle shaft. I'll list all the part numbers for you. Pick from them what you need.

Rear wheel bearing 90363-40020-77 or Nachi 6308-2NSE (96-00) / 90363-40068 or NSK 40BW06CG50 (01-02)
Rear axle retainer 42423-20010 (2 per side)
Snap ring 90520-36045
Outer seal 90313-48001 (96-00) or 90313-54001 (01-02)
Inner seal 90310-50006
O Ring 90301-88077

Whelp pulled the wheel speed sensor and there is definitely gear oil in there... I have seen all the reports of people screwing up the seal the first time, any tips on avoiding this fate?

Drat pulled the other abs sensor and it's both sides which means bad breather likely. I've already got stuff to do the breather mod. Parts price just doubled :*(

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