2008 Denali started chasing exhaust leak

[West 1]

I have already replaced my driver side Exhaust manifold gasket and installed new stainless steel bolts. I did this because I could hear a leak and I could see one broken bolt. Removed the manifold and was lucky the bolt came right out. All done feeling good about the repair. Test drive the dang leak is still there. Left it for a few weeks.

Got back to it today. Passenger side exhaust manifold, rear most bolt was broken but still in place, came off as soon as I touched it. No room in there to drill it so I ordered one of the clamp kits. I have used them before on my 2003 Yukon and they worked for 10 years till I sold that truck.

While in there to get room I removed the plug/coil wires, one was really stuck and came apart on removal. I already have a new set sitting here so no issue with that the truck will get 8 new plug wires.

This truck does not burn oil, the gas mileage is very good for a 6.2L, it already has 145,000 miles on it.

I decided to remove a spark plug just to see what condition the plugs are in. Total shock, these are the original plugs, the plugs on bank 2 all came out with a dark brown on the center electrode? They were dry so they have been firing well which I knew based on the idle quality and the MPG.
Has me wondering if the prior owner who owned a hot rod shop was using an octane booster? I have seen some of the octane boosters stain the plugs like this? I will try and post a picture for you to enjoy.
Using Champion Iridium plugs part # 9405, 7 year warranty on these should be the last set of plugs needed in this truck. The iridium plugs can go 200,000 miles plus and I already had them and a set of Denso wires sitting in the garage. Gave me something to do while waiting for the clamp kit to come in.

Just wanted to replace the gasket and new bolts hoping for a 1-2 hour job and got hooked into most of the day but it appears the truck needed the attention.

 

[West 1]

I can count, I know only 7 showing. The one missing has been replaced and looked new, I actually needed that plug as I had only 7 new Iridium plugs, I have ordered the missing one but it is a week away from delivery so the 1 plug is back in cylinder #1 where I can swap with a new plug when it arrives. The old owner must have had a misfire issue and changed only the one plug? These do have 145,000 miles on them but the heavy brown color is sure odd to me and I have looked at lots of spark plugs over the years. A few of the plugs were not properly tightened and the threads were a little wet with oil/fuel.

 

[OBSandaNNBS]

If the truck was running well, makes me think it's not a problem, you might be onto something with the octane booster idea or other additives.
But that gap tho!!
Did you get the new plug in, how's it running, and is the exhaust leak gone with the clamp kit?

 

[West 1]

I wish I could say it is gone but the dang thing still has the same cold sound like an exhaust leak. Maybe one of the manifolds is cracked but I have not found it yet if that is the case. As soon as the heat comes up the noise is gone till the next cold start. Yep the last 1 plug showed up and has been installed along with new plug wires.