Mine has surface cracks yet works just fine. But you might be on to something with your hydration theory.

What I do (with every hard soap) is add a tablespoon of water or so to the top of the puck and let it soak while I shower. Then I add that water from the puck to my lather bowl, load the brush and begin building my lather, adding more water as necessary. Works great every time.

As a side note, I've had that puck of MWF for probably 4 years now and it's barely dished and has a hard time holding that tbsp of water. At this rate it will probably last until sometime next decade lol