Even if the plugs are good, it's a good idea to change them simply because they have a tendency to sieze in the aluminum heads if left too long. You can imagine how expensive that problem is! 60K is chancy - 100K is way too long, not just for the seizing issue, but for performance from ANY plug, including platinum-tipped. 100K for platinum plugs is only an optimistic marketing advertisement - makes for a good round number. They are typically only good to roughly 60-80K.

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95 E320 Cabriolet, 159K