I have the older mansfield toilet with the white flush valve, and it is constantly running, saturday it was so bad you could hear it a few rooms away. I replaced the red gasket seal but I don't think I needed to it was still flat and not warped or cupped. What made me think it was the red seal was that the water stops when I push down on the flush valve so I thought maybe it wasn't getting a good contact. When I took off the white valve it was smooth on the bottom lip no cracks or pits that I can feel. Any help would be appreciated hope you all have a good day.