This is not a thing you have to worry about. Just start the engine and watch for oil to be dribbling out the nose of each rocker arm within a short time after startup. If not, things weren't cleaned up enough when the head was off.
Do not purchase STP oil "treatment" or any other such goo. It is unnecessary and not beneficial in any way; all it does is waste your money.
Did a visual on valve seals and nothing seems cracked