Spark plug issues

[PEPI]

hi

Changing my spark plugs and all was good while doing the right bank.
When I was doing the left bank I noticed the middle spark plug was very dark and the coil pack shaft had a powdery soot film over it - spark plug was very dark - strong smell of burnt fuel.
When I was doing the last spark plug - taking the coil pack off the shaft snapped off stuck hard and fast - it was completely brittle and powder what was left behind. This was spark plug closest to the firewall.

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As you can see from the pics, a little bit of a phuking pain.....
The spark plugs as you can see the light coloured ones are from the right engine bank.
The two darker ones are from the left engine bank.....last spark plug still stuck in place.
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I will be able to fix issue - order a new coil pack obviously.

Main question is why my left engine bank spark plugs so fouled up? Plugs are 60,xxx km old. I had a slight misfire at idle which was the reason to change them.

Lucky I did I guess - so now I look to everyone for any ideas and/or reasons as to why and what can be done to remedy.

Thanks in advance.

[Spooler]

Those last two cylinder are getting hot. The question is why. Are they running lean? Were the coil packs bad that started the whole issue? Was oil leaking past the valve cover seals?
I would put it back together with 2 new coil packs and read the plugs in 5k miles to see if anything weird is going on.

[Joepro]

Seen this on some cars at work, usually its from the plug being loose and combustion gas cooks the coil, if it backs out far enough it melt the whole coil down. Also curious if the valve cover was leaking.