Had 3 bathrooms re-modeled a year ago and installed these Kohler toilets.  Love the toilets, hate the seals.  I have had to replace the seal in two toilets so far for leaking.  Same as most of the other failures listed here.  Small bubbles form on the surface of the seal and leak causing intermittent toilet running.  Yes it only take 10 minutes to replace the seal but who has time to waste on something that should not need to be replaced so often?   I do not remember replacing the flapper in my old toilets in the 25 years that I owned them.