Objective: how to fix a toilet that fills off and on by itself

Which of the following solutions is more sound in terms of naive physics reasoning?
A toilet that cuts on and off by itself, or runs intermittently, has a problem that plumbers call a phantom flush. The cause is a very slow leak from the tank into the bowl. ... The solution is to drain the tank and bowl, check and clean the flapper seat, and replace the flapper if it's worn or damaged.