Hey Nic,
It must be in the S.C. air, I replaced my timing chain on my 300CD last weekend with great results. Have you ever adjusted the valves on your CD? if so I would compare this to putting in a new timing chain. I looked at my tension rails and they all looked like they had about 3/4 of material on them compared to the new ones I had ordered. So, all I replaced was the timing chain it was 4-5 deg. stretched. I didn't have the equipment to get exact specs on the stretch. I did not want to put in a offset key seemed to be a bandaid for a worn part. My Chain cost $70.00 shipped. Once installed the timing marks were dead on (0). The engine has more pep, better idle, sounds better. My MB independant tech. quoted me 700.00 parts and labor. It took me 6 hours most of it putting it back together, I am a clean freak! The next one i feel I can do in 3 and I know it's done right and how it works. There are certain tools that you will need if you attempt the job. GOOD LUCK.