sptt, distributor cap and rotor should be replaced every 60,000 miles. Unless you have service records for this 1991 300E definitely check the condition of the cap and rotor. If the ignition wires appear old and brittle replace them too, and opt for Beru wires. As I'm sure you are aware that vintage MB automobile will run for hundreds of thousands of miles if maintained properly.

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Fred Hoelzle