On Wed, 26 Oct 2011 23:43:50 -0400, "Stormin Mormon"
wrote:

Fix the flapper is a good idea. Or, you can shut off the
water below the tank. Most toilets have a shut off.

I havn't tried those patches. Fermco coupler might do the
job.

I doubt plaster of paris would make a water tight seal, but
at least it's water activated.
Get a plumber in and replace ALL of the cast iron with Plastic.