If you have changed spark plugs before then it is not much different. 12 plugs and some of them are in tight spots. I have done the job twice on E320s it just takes a few hours. Be sure to get the proper Bosch Platin plugs. The best tool for removing the spark plug boots is a 17mm open end wrench. Moving a few of the coil packs out of the way is necessary but simple.
Just take your time, don't cross thread the plugs and make sure you get the boots fully seated on the new plugs.
Wires push on and pull off nothing fancy.

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tgmiller77
1997 Land Rover Discovery 158,000
1995 E320 Wagon 132,000mi
1999 E320 Wagon 97,000mi