I was planning to replace the float valve on the guest bath's toilet this afternoon, since it had broken down and was running even when the tank was full and the float had moved to the "off" position. Alas, as I was getting ready to do the work, the toilet's water tank cracked. A quick fill-up confirmed my fear: the crack is terminal and leaks. I could empty the tank, dry it out and epoxy the inside but I'd still have a crack on the outside... and if the crack decided to grow I'd have a fresh leak. I would prefer not to take that chance.
As replacement of the tank itself is unlikely, I now embark on a shopping trip for a new toilet.