@aschrauth, pic is OEM from a 150 GD.
I changed once all my fuel line to silicone, and after a while they started to quell.
My advise would be to take from carshop a few meters of their 5mm stuff. Costs nearly to nothing and is quality. There you see 6mm at the caliper, but 5 mm fit tight and aren't leaking.
If you order silicone lines, you have to know the company. Otherwise you do twice.