2002 sport edition, 4X4, 156k miles.

I bought it a few months ago and the first time I was underneath it I noticed the skid plate under the T-case was wet. The idiots who had just serviced the transmission had put a new pan on it, and didn't bother to torque down the drain plug, which was only halfway threaded in. So there was trans fluid all around there and I assumed that was it. Fixed that up, cleaned up everything, good to go. Or so I thought.

Now I notice the skid plate is wet again. It appears to be oil, not trans fluid, and appears to be coming from the T-case. But when I poked around there isn't an obvious source. I figured output shaft seal(s), but there aren't drops of oil hanging out right underneath the seals. It's just wet in general, all the way up to where it bolts onto the transmission. I decided I should see just how dry it is in there and pulled the fill plug. Which, BTW, came loose VERY easy. Like I barely had to put any torque on it at all and I could unscrew it with my fingers from there. But that area didn't appear to be the source. Anyway, it took about a half a quart of oil. But I had the front wheels up on ramps, so I don't know how much that affected it. Obviously it could take a bit more, so I definitely didn't over fill it.

Here's some pics I attempted to take, not much clearance.

I did notice, in the third pic you can see where it's bolted to the frame cross member. On the other side one of those bolts is missing. Gonna look up what bolt that is and get that fixed, probably not a huge deal, but seems odd. Didn't appear to be a bunch of crud and grime in the hole either, so I don't think it was that way from the factory. Which begs the question is this the original T-case? No record in Toyota's service history of it being replaced, but who knows.

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Well, after driving today about 20 miles I see a tiny bit of oil collecting at the bottom of the skid plate. No drips (yet) on the pavement where I park, so I think it's a fairly slow leak. I have never heard any grinding from the T-case, but I hope it is ok. Since I bought it I have had some trouble getting 4WD to engage. It would do it, but I usually had to stop and put it in reverse, let it roll back, and then it would engage. Then when disengaging there was a decent bump, like I went over a small speed bump or something. Well, today I tried it in the parking lot at work and it went in and out of 4WD pretty much instantly with nothing but a click from the T-case, and no bump when disengaging.

In the next week or so I'm going to clean it up real good, then watch it and see if I can pinpoint where the leak is coming from.

The first thing I would do, is check that there is enough gear oil in the transfer case. It's looks to have been leaking for awhile, so eventually the level will get too low. If it's already low, add gear oil until it reaches the bottom of the fill plug hole, while the 4Runner is sitting level front-to-back and side-to-side.

Then clean the T-case housing with brake cleaner, so as you said, it will be easy to pinpoint where it is leaking from.

I feel like I'm in the Twilight Zone. I bought my 02' 4Runner 150K a few months ago, I live in Lancaster, PA, and my Transfer Case looks identical.
Gonna keep up with this thread in hopes of a higher qualified member has answers.

What is a "higher qualified member"?

Someone who has owned a 4 Runner longer than a few months and maybe has a greater mechanical aptitude than me? I can do the basics but I rely on the wonderful world of forums for most stuff. I've spent too much money fixing something after the "trial and error" method.

I just had to replace my front output seal and flange because mine was leaking.

the drips were coming from the bottom of the transfer case but it was wet around the front driveshaft and voila there was my problem, Hope this might help

Ok.

The first thing the OP is going to want to do, is make sure the T-case hasn't lost all of it's gear oil, and is about to grenade from lack of oil.

Then, he needs to know where it is leaking from. As I already said.

Only then can advice be given as to what needs to be done to fix it.