The Bosch ZR-6-SII-3320 plugs are OEM replacements for the USA R172 350, the only difference from the original factory plugs in my car was that they had the Mercedes star symbol on them.Didn't see anything about this in a search.
Looking ahead to a spark plug replacement. The parts sites I'm searching show two different plugs which they both claim to be OEM:
The site says the Bosch are "not for cars that use ethanol fuel", while the NGKs are "for cars that use ethanol fuel".
Anyone have any experience with this? As I mentioned, they both are
referenced with the same OEM part number (004 159 64 03).
If you are interested, here's my write up on swapping out the plugs: http://www.slkworld.com/slk-r172-cl...-ignition-coils-r172-3-5l-v6-m276-engine.html