The leaks could happen any time and could be minor, so I am not sure if you were taken or no. On a different note you say The head was changed, so did they change the radiator and waterpump too? Because if it was the rad, WP and freeze plug you didn’t need a head job as far as I know. I know that Toyota newer 4&6 cylinder engines have issues with the cylinder head bolts coming loose or braking and causing coolant leaks. Just google it. This what your engine could have had and while they were at it they changed the waterpump too. Toyota dealers aren’t known for great service. I only buy parts from them. Also it seems like their quality has taken a turn towards worse at least based on anecdotal evidence.