In the Technical & Restoration Forum in the March / April 2003 The Star Magazine, there is a question about platinum plugs and an interesting reply. It doesn't say who exactly wrote the reply, but it was probably Stu Ritter:

After I put Bosch Platinum +4 spark plugs in my 190E 2.6, a dealership advisor reprimanded me, saying they aren't recommended by Mercedes-Benz. He said that a service bulletin indicated that they should not be used. Is this so?

Some time ago a Mercedes-Benz service bulletin recommended against using fine single-wire platinum electrode spark plugs in their engines. The electrode on these plugs was so thin that the spark could be blown off the plug, causing misfires. The new Bosch +4 spark plugs are not covered by that old bulletin. Thin-wire plugs could cause poor idle quality and misfires at high rpm under full throttle. Mercedes-Benz has not recommended against the newer +4 plugs, which have four electrodes so are not about to have the spark blown off. You might tell your service advisor that serval versions of Bosch platinum plugs exist.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".