There’s no excess or rapid pressurising of the coolant, or coolant loss beyond the known weeps (since 22 year old o-rings don’t take kindly to being disturbed). The whiter plug is from the adjacent cylinder to the one whose piston top is shown. I’d more think the
ECU is leaning out the mix for that cylinder pair until it pings, as a response to the over-rich oxygen sensor readings.
These cars are a huge hassle to get the cylinder head off in-situ, so that’s another reason I really hope it’s not a gasket issue.
