If it has the Korky style fill valve, you can pick up an assembly cap at Lowes for $2.49 and fix it without tools in less then a minute.
Noted that the Toto toilet has been getting sluggish lately. Also the valve shuts of before the water level reaches it suggested mark on the tube and tank.
What is the procedure for adjusting the water level higher. The flush valve is a Toto Power Gravity anti siphon valve. Tank is a 1.6 gal per flush type.