MB plugs are almost always black on the edges of the shell these days.

Those plugs are just worn out, there is nothing else wrong with them, and the gap is now wide enough to give preformance problems, to say nothing of the condition of the center electrode surface!

Non-platinum electrode plugs really need to be replaced at about 30,000 miles, I think, or any time the center electrode begins to round off. The sharp edge of the electrode produces much better spark than a rounded, rough surface, and ignition preformance will decline.

Platinum tip electrode plugs will last much longer, but are only available as resistor plugs and you must adjust the resistance of the entire secondary circuit to compensate -- different suppressors, or different wire -- so that the totat resistance is the same as for non-resistor plugs. May be easy (on my older cars I just substituted non-resistor plug wires), or may be a real pain.

NGK plugs were very well in MB engines, too.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!