Hello,
yes, it's possible from a leaky heater core, to make sure remove the surrounding carpets pressurize the system you must detect the leak because its present you can smell it.
i prefer to use liquid radiator sealant not the powder type, and use good known brand, it can seal only the small leaks. you can try.
https://www.2carpros.com/articles/replace-heater-core
Check our diagrams below how to replace heater.
let us know if you need more help.
thank you.
Images (Click to enlarge)
Friday, February 12th, 2021 AT 10:32 AM