A couple weeks ago the front seat fold on the passenger side of my CLK430 stopped working. The electrical mechanism could still be heard and the headrest could go up and down. As well all the motor forward and tilt still worked. I was able to find the small cable bushing has worn and disengaged, but have been able to repair it.

1. If you need to check you can remove the seat back by removing the two Phillips screw under the bottom and then to pull out slightly at the bottom and then slide the back down and off.
2. Removing the back wasn’t necessary for me.
3. To remove the fold handle - just grab and pull hard straight away from the seat. It should pop off.
4. Remove the snap on cover then, the under plate is held on with one Phillips screw.
5. Push the bushing and collet back to its location with a small pick or screwdriver. Then I added a small amount of super glue to the bushing to ensure it hopefully holds another 10+ years!

 

Interesting. My driver backrest stopped pivoting, and yet like yours, I could hear the motor running when I operated the handle.
I fixed this by removing the back of the seat and adjusting the tension on the steel cords. There is one for each side and you can loosen the steel cords by turning them counter clockwise at the adjustment point. Just like with a bicycle brake line. Video over here which was quite helpful:

Wish my mercedes mechanic would know to do these things...

 

Yes, that’s a great video. I attempted that fix first and it didn’t work, then found the broken bushing near the handle.