I can't say if this applies to MB, and the Techs will correct me if wrong, but if you keep getting an EGR error code check the vacuum lines to the EGR valve closely.
I had another make which kept getting EGR fault codes, could find nothing wrong with the valve, everything working correctly. Once the code was cleared, it would fault within 100 miles. Very close inspection of the vacuum lines to EGR valve revealed that one line had a "pin hole" leak, which was not noticeable until the line was removed from the vehicle and looked at under bright light. Of course you might not be able to see a very small pin hole, but you could pull a vacuum on the line and see if it holds. This occurred in the 100K mileage range, which is right where you're at.
It's worth a check.
73 280 SEL 4.5