Where did you hear that?
Engine oil that’s contaminated with a bit of partly burned gas in it often smells like fuel.
Some of the fuel from the misfiring cylinder will end up in the oil.
The most likely reason for gasoline to find its way to the outside surface of the spark plug and coil is that the spark plug isn’t making a tight seal where it screws into the cylinder. As you say above, that needs to be an air tight seal which stays sealed even for the high pressures that occur in the cylinder during compression and firing. Each cycle the fuel injector squirts a little gasoline which is drawn into the cylinder as the piston goes down, then when the piston goes back up the gasoline would be forced out and onto the upper spark plug surface and coil if the spark plug wasn’t sealing. This would usually create a low-compression misfire and a repetitive tapping or banging noise too.
Yeah… Unfortunately I installed the spark plug and am 100% positive it is both in good condition and properly screwed in. I have had a transmission oil pan leak oil through the threads of the bolt because it was cracked where the bolt screwed in.
Hearing the sound of compression escaping on 5, next to 3 and not on 3 indicates to me that there must be a crack. A crack which is large enough to get fuel on ignition coil 5 and announce its presence on number 3
If air/fuel is escaping from a crack on the top of the head during the piston upstroke, you might be able to figure out where using a length of garden hose as a stethoscope. Or maybe holding something flexible, like a piece of paper or feather, and moving it around to see if it catches the air movement.