Woah... I think you are going to far...
Take just the hub cap off the tag (or front wheels) and you'll see the picture below. Just look at the edges of the clear window for rings labeled "full" and "add" and see where your fluid level is (at the bottom) with respect to those rings. To add gear oil just pry out the blue rubber disk (fingernails or screwdriver) and squeeze the gear lube into that hole.
BTW: The front wheels if drained will hold about 16oz ea., and the tag if drained will hold about 8oz ea. They don't take much.