Cadet 3 defective flapper
We installed a Cadet 3 8 months ago and for the most part, it's been sensational. However, in the last few weeks, we'd hear the tank "topping" up as we approached it. I finally dropped a die tab in the tank and it soon was obvious that the flapper was leaking. I turned off the water, lifted the flapper and felt little bumps on the surface of the rubber ring.
I went to the plumb shop where I bought the toilet, and right away I was told that this was an ongoing issue with American Standard. It seems that the rubber ring is laminated and little "blisters" develop on the surface, causing it to slowly leak down to where the valve opens to top it up.
They gave me a flapper that they have been replacing the defective ones with, because the OEM replacement is in short supply apparently and simply asked me to return the defective one to the store the next time I'm in the area.
BTW, the "area" is London Ontario. The plumb shop is Kitchen & Bath Emporium. Great people to deal with.