You should visit a dealer parts desk for this. I replaced both of those lines a few months ago, and there are many variants depending on what model of vehicle you have, and the age.
It took a good 10 minutes of studying the diagrams on the EPC and looking at what was on my car before we could order the correct part. There are lots of different versions of those lines.
Another thing you should be aware of is that each line ends at a banjo bolt on the side of the radiator. Both bolts are accessible (top one accessed by removing a small inspection hole next to the headlamp, bottom one accessed by dropping the oil cooler down and reaching through the towhook hole). There can be significant corrosion on the union between the banjo bolt and the radiator, that was the source of my leak.
http://forums.mercedesclub.org.uk/showthread.php?t=27902&highlight=leak&page=2