The OE plugs are non-resistor types and anecdotal evidence indicates that resistor plugs can cause idle and/or emissions problems.

The OE plugs had a "heavy duty electrode" as indicated by either a zero or "oh" suffix (I forget which) as in H9DC0. These can be found at Mercedes parts specialists such as Fastlane and probably dealers, but they are more expensive than the standard electrode H9DC.

The "R" prefix in your plugs indicate that they are resistor type.

Non-resistor plugs are rarely stocked by parts stores or repair shops unless they are Mercedes specialists, and although correct non-resistor types are supposedly made by both Champion and Beru in addition to Bosch, I have never found anything other than the correct Bosch.

My suggestion is that you buy a set or two of H9DC from Fastlane and give them you your mechanic to install when they are due for replacement at 30K miles. Most commercial shops will just install a resistor plug, which is not correct.

Correct spark plug replacement numbers are in your owner's manual.

So that's the deal. Whether you chose to install a proper OE recommended plug or continue with the incorrect installed resistor plugs is your call.

Duke