Two toilets have black residue continually forming inside the bowl. Perhaps the braided hoses need to be changed. They are approx. 19 years old. Tried to turn the water shut off valve on one toilet, and had a few drips of water, so stopped. Shut off valves are the same age.
Quite a bit of moisture on the braided hose, but am not sure if it is due to a leak or condensation.