Click this
link for prior history.
Per the thread in the link above, the first time I replaced the spark plug four months ago, the engine's misfiring went away. Today, though, the misfire came back, same cylinder. I replaced the spark plug tonight, but this gave only a very marginal improvement. (Still misfires, but not as badly.)
Aforementioned thread had a recommendation to replace the coil-on-plug, but at $50 each, I'm at the point where I need to get a proper diagnosis. I have no diagnostic tools. One thing that I discovered both times that I replaced the spark plug was that the spark plug well was wet. When I pulled the plug, the part of the plug inside the firing chamber was clean and dry, but the outside part, connected to the coil boot, was wet. Not sure what the wetness was, as there was no discernable odor. When I wiped it with a white paper towel, it stained the towel a light brown color. The engine oil is a darker shade (almost time for oil change). Could there be a gasket problem causing this?
New spark plug didn't fix misfire; now what? 
Threaded Mode
