Misfire Cylinder 4

I recently developed a misfire on cylinder 4 (P0304). I've replaced all plugs and that one coil (Denso for both). Misfire came back so I checked cylinder 4 with a bore scope and it looks like there is coolant in there mixed with the carbon build up and cylinder 2 looks too clean. I've only additionally checked cylinder 1 so far and looks like normal carbon build up. Seems like this is a head gasket issue. Can anyone shed some light? The truck has ~160k miles. Pics of cylinder 4's recently replaced spark plug after driving ~50 miles and bore scope image. Seems to only throw a check engine under a decent amount of throttle and runs fine after clearing the code.

 

I am posting a link below that may give some explanation about what may or might have happened.
https://www.youtube.com/watch?v=dfGTI0sWozc

What year is your truck? The thin metal head gaskets used have a plating on them. When the coolant gets aged it gets acidic, and that wears away the plating on the head gasket and leakage occurs.
Has the oil in the truck been contaminated? Have you noticed a loss of coolant ? The pic of #4 is of the valve, do you have a pic of the piston top? That valve isn't very shiny , the spark plug for 50 miles is clean,
but the particulates are the only thing hinting of a gasket problem. That's high dollar work replacing the HG and who would you trust doing the work ? That's the only real fix,
. Ive heard about new 2 part epoxy HG sealants and read about snake oil , don't know if the epoxy is or isn't what they say it is, but a couple of hundred versus 3 to 5 grand for the fix is the situation you may be in.
I would first do a test of the cooling system to see if any exhaust gasses are passing into the coolant. Need to also check your oil to see if it's becoming milky. If neither of the areas your checking
come out with bad results , what you may have is that you have caught the problem quick and a sealant may work for awhile ,,if indeed the HG is going south . If you go with the epoxy based
product you will also need to check if it is compatible with the coolant used by Toyota or if another coolant must be used. The real fix is to do the work of replacing the HG just saying

 

The more I look at the picture of that spark plug you stated was misfiring , Sir I hope that the head gasket is not the issue. Check for the exhaust gases coming back to the radiator and such and do some testing.
That spark plug looks like it had a whole tube of anti-size caked on it. If I'm not remembering correctly Denso plugs have a coating that doesn't need antisize and with as much on the plug in the pic, could cause
a miss fire. Again , hoping it's not the HG causing the problem

 

Totoro3,
Auto parts stores have cylinder head gasket leak detect kits. You can even get it online. It samples the fumes from the coolant system and checks for contamination with exhaust gas particles that would be introduced due to a faulty head gasket. It's a blue fluid that turns color in the event those exhaust cases are present. It will help reinforce your findings or dismiss them.

Hope that helps b