I just changed the plugs on my 99 CLK430. It wasn't impossible. It took some universal joint adapters and some different extensions to get into the tight spots. I used an open-end wrench to get the spark plug wires off the plug. I took each coil off. I put anti-sieze on each plug and torqued them to 18 I believe. The hardest part was putting the plug wire back on the plug. It just wasn't easy to get them on at the right angle and then I wasn't sure if they were all the way on so I used a couple wrenches to push/leverage them on as hard as I could. The gap was set at 40 from the factory (got the plugs from Phil at Fastlane). I could really tell a difference in the acceleration after the plug change.

__________________
1999 CLK 430
W208
113. Engine
105,000 Miles
Raptor 245/40/17