Earth lead seems fine. Used NGK Platinum plugs.
I haven't had a chance to take the cover off the check the plugs again, but last week's MCSF went off by itself before I got a chance to rset the fault codes.
Alas, it came on again this morning - again after sitting at a constant speed for 15 minutes or so.
When I changed the coils I cleaned out the #1 bore hole, as there was some oil in there, and I noticed that there was oil again when I changed the plugs - not much, but some. This was despite me being very careful & using a funnel when topping up . There is also a rubber o ring/seal - should this be inside the oil cap, on the grey plastic engine cover, or underneath, at the base of the oil filler pipe? I ask because I wonder if some oil might be spilling out from under the oil cap, if this wasn't properly sealed.
Might be a silly idea, but I'll try anything!