Sounds to me like the dealership is trying to shove a big one in you. I say pick up the car. Take it home. Then decide to fix it yourself or go to a different dealer.

Take your car back, Try switching cylinder 5 coil with cylinder 1 coil.

clear codes, see if the code comes back on. If it does, and it says cylinder 1, you know the coils bad.

You can do the same with the spark plugs and injectors.

Did the dealership even try this yet?

Cabin Filter
 

My 2012 370 did not have a cabine filter!

Holy necro-bump, Batman!

May be a forum record!

Damn near a 6 year bump. I'm impressed.

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I'm having same problem as OP. Most times its P0300 sometimes it P0305.
Car runs smooth otherwise.
Does it take a long time to remove things under the hood to get to spark plugs? any special tools other than the spark plug sockets?

T5 bit to remove the screws that hold the throttle bodies on as you will need to remove both throttle bodies to access the number 5 and 6 cylinders