How do you check, change and fill the rear ends oil?
its a 71 12 bolt posi...

You remove the cover to drain the oil.

You fill it by pumping new oil into the square plug hole on the upper passenger side of the differential.

You check it by removing the plug and the level should be slightly below the lip (nothing should run out). Bend you pinky when you inset it through the hole and see where the level is on your finger.

If you put in new gears within tha last 500 or so miles you should change it to get rid of the metal residue from break in.

Chuck