Thank you all. A friend who's a bit mechanical wondered if there wasn't a leaky valve cover gasket resulting in so much oil on the threads, something to look into, though the way the plugs are located under the central bonnet hinge it's actually a little difficult to get a clear line of site down there!
Luddite, I do see your point about the OBD reader surely throwing off a code if there literally was no combustion going on in cylinder #1? That said, if it turns out to be like your Sprite and in the end I get 33% more HP than I'm getting now it will certainly be a silver lining!!
I like your suggestion of just pulling the lead to cylinder #1 to see if it makes a difference, but as you note these GDI engines are "coil on plug" setups and I will proceed with caution (i.e. Googling) before trying that one.
I will check some of the other plugs tomorrow for comparison as per Luddite and Richard's helpful suggestion.
One note -- the suggestion to blow out the area with compressed air before pulling the plugs was invaluable -- it seemed to blast away about half a pound of leaves, dead bees and a number of nuts and seeds -- my car lives outside in a forest and I suspect some small local fauna are setting up camp in the still-warm engine come nightime!
