IMy toilet started 'leaking' as evidenced by it running every few minutes. I replaced the flapper but got the same results. I then bought a new Fluidmaster Pro 45 K replacement kit and replaced both the fill and drain valve assemblies. Guess what, the flapper is still leaking!! The water slowly goes down to just the lip where the flapper should be sealing it, so
I know its leaking thru there. How can this be? The new flapper that came with it seems VERY flexible, maybe too flexible. Help!
You might try draining ALL the water from the tank get it dry ,hairdryer if necessary ,buy a tube of plumbers GOOP at home center, glue that seal over the rim where old flapper seated ,let it dry all nite apply GOOP generosly , it has worked for me .The sticky stuff on bottom of factory seal has to be super dry for it to work and it has to be mashed down over the seat just right