I'm in the same situation right now. I can see the seepage starting. Dealer quoted $160 for the lines and 2.4 hours of labour to install so $615 taxes in (Price in Canadian monopoly money) and they wont cover it under my extended GMPP plan. I hope they revised these things to stop leaking all the time. Truck is a 2017 with only 21,000 miles or 34,000km. Insane.
I found this picture online. Its a piece of trim thats black in color. I was able to use a plastic trim tool and insert foam. Luckily, that solved my nose. Hope this helps.