Smelled gear oil this morning in the garage, leaking out the axle end. I’m thinking rear axle seal. Thoughts?

Rear axle seal or leaking wheel cylinder. Remove the wheel speed sensor on that side and see if the tone ring is dry or not. If the tone ring is dry then it's not a rear axle seal.

Sometimes it's a stuck axle housing breather. Gears get warmed up, air in the axle housing expands, and if it can't go out the breather, it will push past a seal and take oil with it. The little metal cap on the breather (top of the axle housing, on the right side of the center diff housing) needs to freely jiggle.

FWIW the breather on mine was stuck when it initially leaked oil. I freed it up and the leaking stopped, for another 30K miles (more or less), then I had to replace the seal anyhow.

Sensor is wet, and has some iron filings on it.

If you can jack up the rear end and spin the wheel while watching the tone ring that should show if there is gear oil in there. With the amount of fluid shown on the wheel/tire I would expect there to be more gear oil on the sensor. Have you checked your brake fluid level?

I've extended the breather already, and the breather sounds like it's free.

Brake fluid is at normal level. I'll try to get the rear lifted to check sensor ring.

Looks like you’re going to be replacing those axle seals.
How many miles on the truck?

It looks like the ABS tone ring has been touching the sensor? Which means the bearing is probably pretty loose, that might be the real culprit here. It looks a bit chewed on, it shouldn't ever get touched in normal use.

In which case - be aware that Toyota, in its wisdom, has some air gaps in the spacing of the items pressed onto the rear axle (bearing, ABS tone wheel, axle seal sleeve, outside to inside). Most places that do presswork will tend to press everything together, as is the usual case for 99% of situations where multiple things are pressed on. But pressing them all together will leave the seal sleeve too far out to reach the seal, and it will leak again. Just warn the shop, so they can take note and reassemble it the same way.

190k, including a few offroad trips.

Thanks for the heads up. I was watching Tim's video on axle seals, and he recommends turning the retainer 180*. Would that be the alternative solution?

How is the wheel bearing sounding on that wheel? Mine didn't sound good but once it started leaking from the wheel, the noise got really bad to the point where you wouldn't want to take it highway speeds. The metal shavings on the ABS sensor will throw an ABS light too.

I'm guessing it's the axle seal, but if you're still trying to determine if it's gear oil or brake fluid, they have very different smells. Gear oil smell is very distinctive, nothing like brake fluid. Have a whiff, and you'll know instantly.

I did my axle seals last summer at 245k. I did a ton of research on the Dr Coffee method (flipping the retainer). I knew a couple folks that had lots of experience with doing Toyota axle seals that had never heard of doing that, but I insisted because of all the research I did and hearing about people having to redo that job convinced me.

There's more to it, but the basic takeaway is that you need to axle seal to ride right on the center of the retainer. Flipping the retainer seems to be the best way to make sure of this without have to change the location of the retainer too much. In order to make sure you're centered, use the grease test or sharpie test. Remove your old seals, put in the new ones, and do the grease test with your old retainers to give you an idea of where your new retainers will need to be set. Toyota redesigned the axle seals at some point, which seems to be why putting the new retainers in the same location as the old ones doesn't always work out. Make your measurements and mark where you need to press the new retainers, and do the grease test again to make sure the seals are riding in center of the new retainers before putting everything back together.

I'd also order a couple extra seals in case you mess up one or two doing all the grease tests.

I smelled it before I found it, def gear oil, doesn’t smell like brake fluid

There’s been a weird sound, like dragging brake pads, but I’m guessing it was the bearing on its way out. I don’t have a press, or the time/space to mess around with it, going to take it to a shop tomorrow.

Gear oil makes the rear shoes swell and that can be your dragging noise. Either way with that amount of gear oil making its way through the wheel bearing it has definitely washed out the bearing grease. It would be best to replace the wheel bearing when you do the axle seal. Rear shoes will also need replaced and the drum cleaned thoroughly of gear oil.