"T.G. Lambach" wrote in message
...
First of all, where's the short rubber or plastic tube from the valve body
to the overflow drain tube?

Second, the screw on the valve end of the float lever is probably the
adjustment; turn it IN a 1/4 turn and see if that solves the problem.

Otherwise, the "seal" or washer inside the inlet valve ought to be
replaced. $2 +/- at local hardware.
Turn the water OFF.
Remove the little locking tang from valve body, twist the top of the valve
OFF. The rubber seal is before you.

Good pictures!

It has never had the rubber tube and there has been no problem until
recently. No water ever runs out of that opening when the toilet is
flushed, so I don't see what adding a tube to the spout would do.

There is a fill-line marked about an inch or two below the top of the
overflow tube and the problem is that the tank continues to fill past that
mark even when it stops automatcally.
Most of the time the tank will stop filling just as the water starts
spilling into the overflow tube (but even that allows more water than needed
to fill the tank) and other times the float doesn't ever kick up far enough
the to stop the water and I have to lift it by hand.
The stopper is not leaking.

Which adjustment causes the float to rise higher up at a lower water level
so it doesn't keep filling past the fill line?