I just found out a interesting detail about our cars. They have 2 sparkplugs per cylinder. Each pair of plugs has its own coil. I discovered this on the German SLK forum www.mbslk.de . I happen to speak German so I was able to take a look at the postings. They have some excelent information on the Motor including pictures and detailed instructions. I am probably the only one who didn't know about the sparkplugs but I thought I would post it anyhow just in case this wasn't common knowledge.