Thanks Eric, To clarify, the hammer and flat punch was to separate these two parts. It would be called more of a "tapping" than a "hammering". I tapped along the outer edge in a circle a few times and it came off. Also, as you can see there is a blue/green substance on the mating surface that I think may have been sticking the two parts together. I don't know if it is supposed to be there or just something done in a previous repair.
I checked out your links, but they don't provide the info I'm looking for.