Where is my rear axle plug?

This seems like it should be a no brainer, but where do I find the plug to put gear oil in my rear axle? The truck is a 1987 Ranger with AT and 4x4.

It's got a slow drip from the axle and until I take the time to get the seal fixed, I want to top it off but I can't find the plug.

My 94 ranger is located on the front side on gear housing toward the top And I believe it took the square end of my socket extension bar to get the plug out

Thank you. It must be obscured by the T-joint that attaches and splits the two brake lines to the top of the axle.

Its probably a plug that is flush, not something sticking out like a bolt head

And it's probably caked with rust, especially if you live in a Northern climate where things like snow and salt on the roads are a regular occurance. I've been told that you can just use a hammer and tap in the extension bar to get it to work, but I've been scared of getting mine jammed in there, so I haven't tried yet... and the foot of snow and ice on the ground here certainly doesn't encourage crawling around on the ground.