Unknown leak in 1st floor ceiling and wall. Opened plaster wall and ceiling to expose 4″ cast iron waste stack that was cracked, along with the 4″ x 3″ teewye AND 3″ PVC that was inserted into the ferrule of a 4″ lead bend and siliconed in place. After supporting the 3″ cast iron vent stack, we cut out the damaged pipe and replaced.