Rear axle plate?

Hi. I have a 93' Explorer 4x4 and noticed another small problem earlier in the day. There is a plate on the back axle with 10 bolts holding it on that seemed to have gotten dinged a bit and has now formed a small leak at the bottom. The fluid almost looks like brake fluid and I did notice on top is where the brake lines for the rear branch off. My questions are what the proper name of that plate is, what the fluid inside might be and is there any unforseen difficulty in replacing that plate. And info will be greatly appreciated.

differential cover and the fluid is differential fluid