Just go with what the parts dept says is correct, MB did change their mind a few times on the 112/113 engine spark plugs.

It can be a tough job, usually you want to start by removing the air filter box, and also the one screw retaining each coil to the valve cover. There is a special tool "wrench" that is recommended for removing the coil wires from the plugs. Yes, I bet that 113 really is wedged in there.

Gilly