The fact that only cylinder 1 is affected, even after swapping plugs, indicates it is something unique to that cylinder.
I would try swapping cylinder 1 lead over with another lead to see if the problem moves as a first step.
Make sure all leads are securely plugged into all plugs and coil pack.
If you are not certain about the age of the plugs, it might be a good idea to replace them, unless you are confident they are not that old.
Head gasket leaks can let coolant into the cylinder, effectively steam cleaning the plug, where your plug is showing whitish deposits, which can indicate it is running hot or lean, which might be a partially blocked injector on cylinder one or possibly the injector seal on cylinder one leaking.
You could try spraying some carby cleaner on injector 1, to see if that changes anything.
If you look behind the A/C compressor you can see injector 1, I would do that with cold engine idling so you are not spraying a solvent on a hot engine.
I don't think it would be MAF or 02 sensor related, as that would affect more than one plug.
Are you seeing any air bubbles entering the expansion tank from the return hose while the engine is running?
I would keep an eye on the coolant over a few days, check the coolant level every morning while it is cold to see if there is any coolant loss which might indicate a coolant leak or head gasket issues.
Hope that is of some help or at least a start.
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