Help: Differential Cover Drain Plug Question

Discovered today that I'm leaking differential fluid. It appears to be seeping out right through the rusted differential cover. Unfortunately, someone has previously stripped out the fill plug, so I can't even check the level, let alone refill it when I pull off the diff cover.

I'm looking at a Dorman replacement cover that has a drain plug on it. I'm wondering if it would be possible to use the drain plug as a fill plug as well. Just wondering if anyone has ever done this, or has any other suggestions for me. Thanks!

As far as I remember it only has one plug. You fill it to the bottom of the whole and yer done.

Cool, thanks. So they shoud really call it a fill plug, not a drain plug...