I have a 1995 E420. Had it at my local Bosch authorized garage approx. 1 1/2 years ago for scheduled maintenance (approx. 85,000 miles on odometer then) and the master mechanic recommended flushing out the burn chambers. He explained that over the years and mileage, carbon deposits in the burn chambers and distorts the flow of air/fuel and lessens the intensity of the burn...thus, less power produced in each cylinder's burn chamber. I had been noticing over time that my car had become sluggish. Just didn't have the "get up and go" that it had when I bought it Starmarked with 36,000 miles. He had some sort of machine that flushed a chemical or solvent in the chambers. Car was like a rocket after that. This, of course, assumes that everything else has been maintained properly... timing properly set, good plugs and gapped properly, clean rotors, clean air filters, etc.

Perhaps someone on this forum can explain the burn chamber flush more technically. Good luck.