I did the entire job in less than 1 hour on my 98 ML320. As previously suggested, removing the air filter box makes it easier to get to the plugs for sure. I bought a K-D Tool spark plug wire puller pliers at O'Reilly Auto Parts for $14.00 and it made easy work of the removing the wires. Be sure to use the pliers on the metal portion of the leads ONLY, and use a twisting motion. The plugs were the original plugs in mine, but I had no problem with seizing. My best recommendation is to remove and replace the plugs only when the engine is dead COLD. That is an old piece of sage wisdom from the advent of aluminum heads, and applies on your all-aluminum M112. Labeling the coils and wires isn't necessary, but would be useful if you find a plug whose condition differs from the others, and want to further test the wires and or/coil. If you have a multi-meter, it wouldn't hurt to test the wires resistance (they should be 2Kohm per the marking on the leads).