My white pan is pretty good, but my black pan is a mess of chunks that you need to add water to at least ten minutes before you plan to use it. That's the other trouble I've had with gouache in pans: not all colors rehydrate the same.

I've heard you can add a little vegetable glycerin to the pan to keep it from cracking as much. I don't typically paint with dried gouache, but I know what you mean how some dry and shatter spectacularly.