I got the rear diff cover off finally by doing this:
Hammering a razor blade in there was enough to break the initial seal. If you use a 2nd razor blade, put it behind the first one. I still didn't have enough space to get a screw driver in between the blades, and the blades were going further and further into the diff. I took some pliers, removed the 2 blades, and of course 1 of them fell in the catch basin. After I fished it out and dried it off, I hammered in that razor blade in spot that was just over from the first place. At that point, I got a small pry bar behind the blade and that was enough leverage to break it fully open.
Today, I don't have much to do on the Jeep. The new transmission pan and Lube Locker diff gaskets will be here tomorrow. I may clean out the diffs more, and clean out the RTV, but that's it. That shouldn't be more than an hour.
For now, I have some coffee and The Righteous Gemstones to watch.