I was having the same issue as the gentleman & i noticed quite a bit of oil residue on my plug & in the well. Do i have a valvke cover leak you think?How does the bottom of the #1 plug well look? Is there any oil down there? The 1.8's are prone to valve cover leaks which allow oil to seep into the well and short out the coil, which can damage it, as well as causing a misfire.
As I recall, the gen1 1.4T valve cover gaskets are prone to doing that, too. (Hopefully somebody with one will chime in here.)
When you swapped plugs and replaced the coil module, did you notice any oil on the #1 boot?