I would also like to add my thanks to WhiteRabbit for a great write up. I've been wrenching on cars for many years, but it's always nice to have some guidance on where to start and what pitfalls to watch out for.
A couple of notes from my experience that I would like to share:
1. I also had a heck of a time with the wiring sockets on the coils. About the third time a gray locking tab shot out of the engine compartment or broke off, I decided to leave the connectors in place. The wires have plenty of slack to keep the coils from interfering with removal and installation of the spark plugs. This made my life much easier and saved me a lot of time.
2. The OEM plugs have a "fat" insulator that allows the boot to seat properly. As edgalang mentioned, there is no "snap" to grab the tip of the plug inside the boot, the rubber acts like a "Chinese finger trap." (Great analogy!) The problem I had was with the aftermarket plugs (both Denso and Champion). They have a slightly thinner insulator. This causes problems with the grip and, together with the dielectric grease, does not allow for sufficient friction to make good contact with the conductor. I noticed the difference when I first saw the new plugs, but it didn't dawn on me that would be an issue until I installed them and could not get rid of the misfires. I'm glad I decided to try out the "easy" side first. For the record, the OEMs measure .040 inch and the aftermarkets .035 inch.
3. With regard to swinging the air box up and away. I found it helped to grab the rubber hose on the intake side of the clamp until the air box was perpendicular to its original location. This kept the accordion hose from kinking until the grip "broke" and the air box tube started to turn.
4. What's up with that back torx screw on the air filter housing? Next time I will replace it with a hex head screw that can be easily removed with an offset wrench.
I hope these observations make sense and will help the next DIYer that takes on the job of replacing their plugs.
Enjoy your Mercedes!
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