Sounds like you will need a new or rebuilt driveshaft. You may be able to find a split boot to temparaily repair it. But clunking is usually a sign of damage and worn metal. I don't know if they make the split boots for a Mercedes. I used some on a '78 Honda Civic. I treied the motormite ones. I didn't like them. The little screws to hold the boot together don't do well. I bought some from Car Quest (I think). The seam was glued together. They seamed to hold up. The kits come with CV grease. I think you can buy CV grease separtely. I'd clean out the joint with brake cleaner after removing as much grease as you can.
But thats a temporary fix. I think you need a rebuilt drive shaft.
Tom