Davestlouis,

(Good to "see" you on this forum!)

It is NOT a myth with the older Benzes. I believe it has to do with the higher temperature range of the Platinum plugs. You want the right amount of spark at the right temp for your specific engine. More is not always better! And in this case it turns out that "better" isn't even always better! I would look it up in my service or owners manual and give a nice techy answer, but I'm afraid I accidentally left them both at my parents' house on my last visit (oh well, it's just added incentive to see them again soon!).
Mike

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Love driving my '77 450 SEL!
124,000 miles