Well, you could just pull a plug and see what's in there assumming your happy now. The plug installed at the factory is listed in the back of the owners manual but after 19 years it may have been replaced by a newer number. Most MB OEM plugs are Bosch so you can also go to the Bosch site (google) and input your car/model/year and see what's recommended. Some people prefer the single electrode plug. Generally the recommendations start with the multi-electrode so scroll down to find the single electrode plug rec if that matters to you. Good luck.