Spark plug carbon tracking

99 - 65k miles - sorry for the long post.
I am one of the unlucky ones that has had numerous bouts of misfiring, surging, hesitation.

Last fall the dealer had a tough time finding a problem but blamed all issues on bad wires. I had replaced the plugs myself prior to the dealer visit and the problem kept re-occurring shortly after plug replacement.

The dealer replaced the wires, I felt stupid and I was on my way. Low and behold the problem was back two days later. Dealer then says I have a bad plug number 3. They replace it and two days later problem is back. They then do another full inspection and determine all is good and this should not be happening. They pull out another plug and this thing has a major "carbon track" down the white insulator( spark is jumping around the plug insulator. They replace the plug and put some paste in each of the other boots and the problem disappeared for the winter.

It is back again. These are all Delco wires/plugs.

With all that said, I bet others that have the same notorious similar issues will have this carbon tracking on their plug(s).

Does anyone know what can cause carbon tracking on the plug to mysteriously reappear time and time again? I am starting to think that when the plugs weaken a faulty/clogged EGR can cause too much exhaust mixture in the cylinder during firing.

This is an excerpt from another car forum:
"Carbon tracking on the insulator around the center electrode is evident on the first spark plug that was removed. The spark was lighting the mix as long as no EGR was present, but adding recirculated exhaust gas to the cylinders produced annoying random misfires. Eliminating the EGR fooled us into thinking the EGR was the problem when actually it was only magnifying a concern that was, in effect, unnoticeable when EGR wasn’t flowing. Any deposit that weakens the spark of a particular plug can cause a surge/skip that EGR may magnify. Because EGR feeds inert gas back into the mix, a cylinder with a weak spark due to spark plug problems might fire just fine without EGR"

Thanks for any input.....

That could be it. Or before I read that, I thought maybe something with the spark plug threading or the threading on the block. Faulty threading could possibly allow combustion to be occuring up next to the spark plug casing.