Re: which spark plugs and where to get them?
Just make sure you don't allow dirt into the threads or the cylinders.
Take off the plastic rocker cover (4 torx screws), remove the screws holding each coil, remove the screws holding the plate that the coils fit to (note the one top right also attaches the earth lead). Juggle the wires out of clips, and detach the four plugs to the coils. Mine already had paint dabs on them to show where they go back. Mark yours if they haven't. You need to lift up the plastic clips to release these plugs. Pull up the 4 coils and 4 other plug caps to dislocate them from the plugs, then lift the whole lot off (plate, coils and caps). Now you will be able to see the plugs in the head. Blow out any debris with compressed air. You'll need a 3/8 drive plug spanner on a 12 inch extension. Note the hexagons on the plugs are the small size (motorbike type).