yeah i'm having same problem, i was thinking to remove the bolts , without disconnecting idk if that's possible i will try tomorrow .

 

Might try to get a screwdriver inbetween the 2 parts of the connector and twist it to separate the wiring from the coil. I had problems with my car, same place, also.

 

ok so i replaced all spark plugs today without damaging anything. So basically what needs to be done is :
1 .open that grey connector, slide it to right press it hard down + push black peace to right to unplug it ! has to be at same time press grey thingy and slide black piece! do that with all connectors, after that disconnect and put aside entire wire system that sits on a fuel rail to make space because when you ll pull coil pack out it will req. more space
2. unscrew 2 bolts that hold the coil. Same processes for all coils
3. Grab head of coil , wiggle it and try to make vision on the boot so you can stick thick plier grab the boot and at the same time pull the head of coil with the boot using the plier ( Its a very dangerous process , i got lucky didnt brake any of those boots or coils but even if you break the boot Mercedes sells it on the dealer 25-35$ )
4. once you got it out you need to use 14mm socket and find mutliple extenders for this process because in first 1-4 cylinders extender fits barely. In back cylinders 5-8 very limited space hard even to get the socket it, just need to be patient and use some hand skills ( Its possible )


Did this process first time in my garage took me 4 hours . (not good not Bad)