You can order a replacement line from this site or from your local Mercedes dealer. You didn't say which injector it was so here are the part numbers for each cylinder. Just select 'Fastlane' from the 'Buy Part's link at the top of this page and search for the part number you need in the 'Parts we stock' box on the left of the page.

6010702333 Cylinder1
6010702433 Cylinder2
6010703633 Cylinder3
6010702633 Cylinder4
6020700433 Cylinder5
6030700433 Cylinder6