Just glue it back together with CA, lap it, and use it. I have a half width naniwa 3k/8k I got it from a friend, and it broke while in the post in the middle. I glued it back together with CA, lapped both sides flat, and use it without any issues since then, and this is a stone without base. I am fairly sure you won't have any problems with the stone, mine was glued back maybe 3-4 years ago.