As you know I own(ed) a combo stone, an Oishi 1000/6000 that I considered a nice little stone for the price, it was my first stone with "polishing" qualities and if you look back in my posts you'll see that it came in my first order along with my mac, my Idahone rod and some more stuff.
I was happy with the stone, specially considering the price ($31 from Theepicureanedge.com).
But since long ago it started getting some crackling signs, specially were both stones were glued (as if they were going to separate), but I didn't pay enough attention to it, and since I own other stones that are much bigger and better, I just left the Oishi for my cooks, but now, as a result for being soaked very often and to get dry in a very warm place (My kitchen is kinda hot) it crumbled like pate brisee, and now it's totally useless, it crumbled on the sides,and it became uneven (as if it were swollen) on the sharpening surfaces.
I don't know if that happens to other brands of combo stones, or if only the Oishi is prone to that kind of issue. If someone owns such a stone, just take care on the soaking/drying process, I don't know if that happened based on the times that it was soaked, or if it's a direct result of drying in a warm environment.
Take care and let me know your toughts.