Welcome to the world of owning a euro car in the US, it's gonna be hard to find certain parts. And that's going to be one of them. I too believe that is a vent. To check, pull the under dash panel on the drivers side and look for a black line that isn't connected to anything. Wiggle the one in the engine bay to confirm that they are indeed the same line. If this is the case I wouldn't worry about changing the connector. If not they it's time for more searching.

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