It sounds like I would probably be best served to leave the 5K wires in place and try some non-resistor plugs as a starting point. I was only concerned about this as going through the cars logs, it seemed like there were a fair number of fairly low mileage (under 5K miles on the plugs) plug failures in the last 20 years.

I know these old Mercedes were not the easiest on plugs, but I would expect more than 5K miles out of a set of modern plugs. I am guessing getting away from the resistor Champions and going non-resistor NGK's will hopefully help longevity. If not I will try bumping up to the next hotter plug.

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1973 Mercedes 280 "Strich Acht Dunkle Rot"