Maybe¿? This thread prompted me to do some more reading. Apparently there can be some internal leakage, so that could very well be burn marks/blow through. It's been ages since I replaced plugs, usually on the motorcycles. Albeit, last bikes were sold/traded before plugs were due. I'd say follow torque instructions to the letter - ie, some say bottom out then 1/4 or 1/2 turn, others give a specific torque value.

 

That is moisture cycles. Usually in colder climates you see a lot of moisture in the spark plug holes. Typically most coil on plug setups are engineered to block outside contaminants. This same seal will seal the outside with the inside.
So many times as the engine is warming up it will heat up the air in this tube and cause condensation. Many folks have seen this. This condensation just coats everything in there and will sit on everything until it the engine heats up and can evaporate this.
As the car sits over time it develops more condensation, and will start attacking. The reason it looks like this is because there is moisture in between the ceramic and the metal surrounding it and as it warms up and starts evaporating some of the rust will start to follow as well.

New sets of plugs will do the job, make sure you take apart your coil tubes and clean them properly as well. It could help to do this on a hot/dry day.

 

Anybody **** with pulstar spark plugs?

 

Replaced spark plugs at 97K miles. These were installed at 47K miles, so they had a 50K miles run on them. While unscrewing they were squeaking bad and threads appeared oxidized, so I put a light coat of anti-seize on the new spark plugs. Adjusted the gap to 0.043 inches per owner's manual specification. Added a little bit of dielectric grease at the opening of each spark plug boot. Torqued to 14ft-lbs per FSM. Cleaned throttle bodies and peeked inside the cylinders while at it. The car continues to run great.

 

Nice. Need to ask Santa for one of these as an endoscope is a cool toy for those with OCD:
We are looking at the bottom of the exhaust/intake valves? Or maybe a set of intake/exhaust as we have two for each.

 

Did they change anything in later year models? I had a surprising number of 10mm bolts to take off for there having been no mention of needing a 10mm socket. Also follow steps 2-8 to complete the opposite side was doing a lot of lifting. Mostly similar but I had different things needing to be taken off, and the last coil back didn't have enough slack to pull out because of the short connector cable forked off of it. I guess still thanks to OP for mostly getting us there 13 years ago.