antifreeze is leaking

1.Heater core drain not connected properly. 2.Heater core is defective. 3.Heater core connectors are in poor condition. 4.Tech didn't recheck after the repair.

agree w/ S/B imports-only choices- heater core damaged upon installation/poor heater hose connection or use of auto zone heater core.

Very likely the junction where the core is connected to the coolant pipes. There are o-rings and seals that need to be removed and installed properly. Also, if there any scratches in the junction housing it will leak.