In the pics, there appears to be a black o-ring/seal - it should not exist there.

 

Well yeah, cause the diff clutches would be toast and more then likely the gears would be damaged. Really depends on how low it got. When you drain it, because you must, you should measure how much comes out. What goes in will be about 1.5 quarts or so. Either way, you need two quarts of proper carbon clutch compatible fluid - or again, the clutch pack will burn up. Rover sells the fluid or you can get GM equivalent 92184900, which is used on GTOs with carbon clutches, but the GM fluid is cheaper and usually easier to find at Napa and such.

 

That black o-ring looked copper in the light
And your right on drain and fill plug

 

Well either way, that o-ring should not exist. The only thing I do with drain/fill plugs on the diff is put some teflon tape on them - the same tape used for pluming. Dirt cheap and helps prevent leaks.

 

Orlando Land Rover is $103 for plug and 2 quarts

 

The plug is like a $5 part. The fluid maybe $60 for two quarts if you go GM. You can also try to find Castrol BOT 720 - rare stuff, very good, no longer made. I suggest calling your local Napa, etc. The big chains don't usually carry the GM stuff. Its a bit of a specialty item. If you find Castrol, it will be old stock which is fine but you might get a good deal if someone wants it gone.

edit:

 

I love my old LR3... but among smaller things, have a strong feeling rear locking diff needs a rebuild plus E motor... followed by front diff rebuild
What would be a fair price for parts (rebuilt) and labor on:
Rear locking diff
Front diff

Would you go rebuild or chance used?

 

Someone else will have to answer that cause I do all my own work. So no clue on paying someone to do it. But parts along run into the hundreds. I think a front diff along can be about $2-$300 in parts.

 

can I ship you a project? LOL

 

I barely have time to fix my own! LOL