If you were going to the doctor, they would ask you to fill out their medical history form.
This can help with diagnosis. You might consider doing the same thing.

The engine may have 180,000 miles, but what is the maintenance history. For instance, my '92 300E has 242,000 miles, but all the ignition components are relatively new.

You would probably be best served by simply making an appointment to have you car scoped at a MB independent shop. That will be more cost effective than throwing parts at the problem.

Steve