Rear diff started leaking. How stop it ?

so,If I'm seeing this correctly- Its not a simple Pinion Seal?

 

Front should be around 4.5 gallons with power-divider. Rear will hold about a gallon less. Most 40K sets on highway diffs hold around this amount.

Take your time a choose a high quality RTV sealant for this joint. Loctite all fasteners, use new lock washers and make sure they get tight. Recheck the bolt torque after a few heat cycles to make sure they remain tight. Clean and dry when the sealant is applied, otherwise you'll be in there again.

Unlike Dana, Meritor has nice new bolt kits available for diff install with Loctite already applied. Your dealer should be able to order the bolt kit by serial number.

 

That's not too bad yet. I don't see it causing problems for a while. Two drops a min will leave a dinner plate sized puddle after a 10 hour break and you can still touch the oil level with a finger through the fill plug in the morning.

 

All good advice.
One more thing check the vent up on the axel tube going out towards the tires.
Sometimes they get plugged up with road debris and the the differential builds up internal pressure causing leaks.
Doesn’t sound like a big enough leak to keep you from getting where you need to go with it.
A small amount of oil can really spread on a flat surface creating the illusion that it’s much more than it really is.

 

Yup. If it’s below the oil line because it can’t be seeping obviously duringcure process But if it’s above, red rtv will seal it for a long time. That’s what I use

 

RTV ultra black is my go to sealer.
I have it in caulking gun style tubes because we use so much of it in the transmission shop.
I also used it on the rear structure of my 14.0 liter Detroit and it’s still dry as a bone 4 years later nock on wood.