Heater core?

Hello,

It does sound like you have a leak from the heater core. Now the leak can be from the actual heater core or the hoses that goes in and out of the heater core.
The heater core is located behind the instrument panel between the air inlet duct.

The heater core consists of fins and tubes arranged to extract heat from the engine coolant and transfer it to air passing through the heater core.

Here are couple of helpful articles:

https://www.2carpros.com/articles/replace-heater-core
https://www.2carpros.com/articles/replace-heater-hoses

I have also attached the heater core replacement for your reference.

Please let me know of any questions.

Thank you.