[sanghill]

Refer to this post: vent tube in LR wheel well
My guess is you can't get a hose into the RDU far enough to remove much oil.
The oil is clean and doesn't wear out. All of the metal filings are attached to the magnetic fill plug(s).

 

[sanghill]

Thanks for the correction.

 

[sanghill]

Both answers are correct, there are 2 fill plugs on the rear of the RDU for special gear oil.
The only way to change the ATF is to lower the RDU, remove the cover plate and then you can change the ATF.
The only important thing to do is make sure the gear oil is topped up and you wipe the metal filings off of the fill plugs.

 

[sanghill]

Bleed it with a wiTECH.
Which Cherokee do you have?
Only the Trailhawk uses ATF fluid.

 

[sanghill]

1. Both sides are gear oil. ATF can only be accessed by dropping the RDM and removing the cover plate.
2. Remove the fill plug with difficulty. It can be done.
3. Top it up. Then you will know how low on gear oil you are. Wipe off the magnets and note the amount of filings.
4. Don't need to drop the RDM. Remove the axles and replace 2 seals. My estimate at least $1k parts, labor and all the other costs.

Post #7: You can remove the sensor to drain the ATF, but you can only add ATF by dropping the RDM and removing the cover plate.

My gloom and doom prediction: You need a new RDM. My left rear axle seals have leaked since it was new.
Every year I add a couple ounces of gear oil.

This is a related Post: Rear Differential chattering, binding, when turning...

 

[sanghill]

This is one of my Posts: vent tube in LR wheel well
This is my Post about insulating the tail pipe. Rear axle weep
In my opinion, after doing it, insulating the exhaust pipe serves no useful purpose.
Refer to your last picture above:
The vent with the red cap is for the gear oil portion of the RDM and vents to the left rear wheel well behind the splash panel.
The vent on the black cover is for the ATF chamber, I don't know where it vents to.
Exhaust heat does not contribute to building up pressure in the RDM, I tested for that.
The axle seals on the left and right are the same. The reason why the left side weeps/leaks is because the oil level on the left side is higher.
This is because the oil migrates slowly from the right side to the left side.
Once I filled both sides completely full to the bottom of the fill holes. The next time I added oil the oil poured out of the left side. I had to add oil to the right side.
If you remove the left fill plug and no oil comes out it is really low and the right side is probably close to empty.
When you add gear oil measure how much you add to the left and right side separately.
You should be able to add more to the right side than the left side, if not then probably the unit is nearly empty.
Use the measurement marks on side of the bottle.

Go ahead and add gear oil to both sides, think positive.

 

[sanghill]

Reference #2 above, I am pretty sure it is a 3/8".

Refer to: Is this normal for rdu? Post #5.

 

[sanghill]

Just used my ruler, it is 3/8"