Significant automatic transmission leaks

[jangell]

I put a quart of fluid in my automatic a month ago. Yesterday I put in another full quart when I noticed it slip slightly when cold. That can't be good.

After about 10 minutes of driving last night, I put some cardboard under the car. I checked it about 16 hours later, and I found this:
IMG_2484.jpg

I've marked up where I think the fluid dripped from here:
IMG_2486.jpg
- The centerline drops are just the low point where the leak collected before dripping down
- The pan isn't actually leaking (of any note, anyway) -- I cleaned that up quite well and properly torqued the bolts and everything. It's in very good shape. I think it's just that some fluid collected there and leaked off of it.
- The cooler is still leaking a little. I've just been dealing with it, because it's not leaking a lot.
- The majority of the leak seems to be coming from the driver's side of the final drive near the axle. The entire bottom of the torque converter housing (whatever that part of the trans is called) is wet. I think it's in a line because that cardboard was a bit warped, so it drained to the lowest point.

I want to be clear that I don't know if this is final drive fluid or transmission fluid. I'm thinking final drive fluid, but I'm not totally sure; I'm not good at identifying car fluids.

More pictures from under the car:
- Wet casing below the torque converter casing thing. You can also see the drips on the centerline near the drain plug for the final drive.
IMG_2487.jpg
- The leak has even gotten onto the subframe under the engine.
IMG_2488.jpg
- The pan looks fine. I think the liquid on it is just condensation (water). Not quite sure what those black oil-like flecks on the blue joint for the coolant hose are, though. It seems the e-brake line is rubbing against the edge of the pan, so it might be that it's wearing away/melting the rubber and causing it to "splash", but that doesn't seem right...
IMG_2489.jpg
- The ever-present trans cooler leak. I'll get that nut tight enough someday... or replace it with an alternate cooler.
IMG_2491.jpg
- Drips from the final drive. That black thing with the wires is the hall sensor for my speedometer. The green-brown fluid is final drive fluid.
IMG_2492.jpg

The thing is, this doesn't like like trans fluid to me, but rather gear oil. I replaced the driver's side drive flange a couple months ago, which did seem to reduce the leaking at that point, but this is notably worse. Today I raised the car up on all corners, making sure it was level, and removed the final drive fill plug, and immediately fluid poured out. I had filled this when I replaced the flange, and it was only full to the bottom of the fill hole.

My friend theorized that a seal between the transmission and the final drive has failed, and that transmission fluid is getting into the final drive, which in turn is forcing out the gear oil.

I'm tempted to remove the final drive fill plug and catch all the fluid that comes out, just to see how much extra is in there.

Has anyone seen this kind of thing before, and any idea what it might be? Is it some seal between the trans and final drive? I notice a lot of automatic transmission parts aren't available, and I don't want to buy another one (I'm on my fifth; I'm getting tired of this, and this one only has like 5k miles on it), so hopefully this is a fix that doesn't require special tools with available parts.

I was hoping I wouldn't have any real drivetrain problems for another 5 years or so, when electric conversions were more affordable and I could ditch this garbage transmission once and for all, but we're not quite there yet.

Thanks!

-- Joe