Last week Mary reported the toilet in the front bathroom had the sound of running water, which is unfortunately the sort of noise I can no longer hear. I replaced the flush (a.k.a. “flapper”) valve, because it’s always the flush valve, cleaned the valve seat, washed my hands vigorously, cauterized both stumps, and declared victory.
This week she reported it was once again leaking.
A bit of poking around showed the tank was now full to the top of the overflow pipe and the refill tube was piddling down the pipe: obviously, something was wrong with the fill valve, because the flush valve was sealed tight.
Having been through this rodeo a few times, I fetched a replacement valve disk from the Box o’ Toilet Stuff, installed it, and was about to declare victory when I noticed the refill tube was still piddling.
Pop the top off the fill valve and peer inside:
Did you see it? I didn’t, either, when I replaced the valve disk.
More fiddling produced this view:
The valve seat is attached to a plastic stem going down the length of the fill tube, but it’s free to rotate on both ends. I have no idea what applied enough torque or how it could break all those ribs, but there they were(n’t).
Fetch a complete valve kit from the aforementioned Box, drain the tank, install All. The. Parts., verify that the valve now shuts off properly, declare victory, etc, etc.
Whereupon I could switch caps and begin making the weekly pizza.
Never a dull moment around here …
The Smell of Molten Projects in the Morning 
our fill valve has begun making a shrieking sound as it fills. I’m sure you could hear that. :/
I thought it was just my tinnitus changing pitch …
Went with the “pressure assist” toilets years ago:
https://www.build.com/product/summary/561052?uid=224619
They are great and can sink any Ohio class submarine that got dropped in there.
Plus they use only tiny amounts of water.
First time I fired one of those pressurized crappers, I thought the world was about to end. Definitely not a subtle thing in the middle of the night …
Meh. After a few weeks we did not notice it any more than the old flush toilets.
Bonus: have not needed a plunger in decades.
I had an entire flapper valve assembly spontaneously snap off at the base inside the tank. This caused a full water pressure stream to enter the tank against the underside of the tank cover. It just happened to wake me up in the middle of the night. Sure glad I was home when it happened to just shut off the valve and replace it later.
We have two generations of the American Standard Champion toilet. The older one is the 1.6 gallon and the newer the 1.28 gpf. I noticed that the ADA “comfort height” toilets have a better “flush number”, presumably due to increased siphonage (totally a word), and our aging knees prefer the height.
All this leads to the valves. No flapper, more of a cylindrical dead lift. These are circa 2012 and 2014. I’m tempting Murphy, but no failures in either toilet in the dump and fill valves. OTOH, they’re a pain if one installs the toilets assembled. Far easier to install the stool, then do the tank. I got a not-so-subtle reminder when we redid the bathroom floors.