I replaced the flush valve assembly in a Kohler Wellworth toilet today. The existing valve was sticking and causing the toilet to run constantly. I turned off the water supply, drained the tank, and removed the old valve using a flush valve socket wrench. The new Fluidmaster 504 valve was installed along with a fresh tank to bowl gasket. After reassembling and turning the water back on, the toilet now flushes properly with no running issues.