It is well established we should not use those new-fangled plugs on our older Benzes. Use the ones that are recommended for your car. This is a link to a post made by one of the old time experts who unfortunately is no longer with us. http://www.peachparts.com/shopforum/27288-post6.html

Resistor plugs actually work fine, at least on the M117 Djet. I ran my 72 Djet for 20 years with them. But the general thinking is to use non-resistor plugs and that is what I am now doing (without any noticeable improvement )

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5