AMGtech has been banging the drum lately about M278 issues, and even gave me tips on how and where to look. I pulled one cam position sensor on the driver’s side, and it was dry. Then, a cam adjuster magnet on the same side - it seemed a little damp. Next was the top cam position sensor on the passenger side, which is this:
It should not be shiny, and my fingers shouldn’t be covered in oil from pulling it...
Now to call the dealer and get a loaner. Wish me luck peeps - this can range from new sensors, to a new engine harness, to a new engine. Or all of the above.