coolant leaking behind the firewall - heater core?

Hello, I'm Danny.

Here is the information you requested. Here is a tutorial showing how to replace a heater core:

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

I would check the heater core hoses first at the firewall to see if it is a bad or leaking connection first. I've attached picture steps below on how to replace the heater core on your Jetta. Hope this helps and thanks for using 2CarPros.