Diff Fill Plug?
Bottom half with a square head indention in it? If that's it how do you get that thing out? Man I miss the cars from the 60s
A 3/8" or 1/2" extension on a ratchet should fit in there. I can't remember what size it is for sure.
just curious why you are adding modifier to existing fluid that should already have it in there. one wheel peel?


