The Cam Sensor issue is where the sensors around the balance shaft indicates the balance shaft is out of round. It's pretty common on the W211 E350 3.5L V6 like we have. My CEL came on and the shop explained the Balance Shaft Issue along with a problem I have with solenoids on the intake manifold. They said the solenoids come assembled with the Intake Manifold making it an expensive replacement (as usual). The cam issue is a common one and should appear if you google it. Here's a good explanation: You are being redirected...

I have had MBs for nearly 30 years. I started with a W108 gas (280S) and then bought my real love - a W123 240D followed by a W124 1991 300D which I consider to be one of the best cars MB ever made. I also had a 73 280SE 4.5 which was an awesome car - I've heard rumors that MB engineers consider it to be the best MB ever made. My money is on the W124 300D. That diesel was rock solid and easy to work on. It's at 275k Miles now and I hope to keep it on the road forever.

It seems like MB has had increasing quality problems over the last 20 years. I fear passenger car diesels are over after the VW cheating problem.

Good luck!
LarryT