Check the condensation drain port\tube on the passenger side lower firewall and see if it's dripping green stuff.
Or just look for spots on the ground in that area that are slimey and don't evaporate; that's antifreeze.
Most common cause is the barb where the heater hoses connect in the engine bay crack at the end tanks. It's either going to be plastic or cheap cast powdered aluminum and not readily repairable. Even if you can repair it, you're still looking at pulling the dash apart to pull the HVAC box out to get to the heater core, and this could involve discharging the AC system (the evaporator core is in the same box) and draining coolant.
If you are lucky, the manufacturer provides an access panel in the HVAC box to pull the heater core/evaporator/blower motor, etc out from under the passenger dash or behind the glove box. If you are unlucky, you need to remove the entire dash and remove the HVAC box as a whole unit first.
Quick fix if you don't need heat is to pull both heater hoses from the firewall and bypass the heater core: join the hoses with a small section of pipe and two hose clamps.