So from looking at the oily residue in the runners leading to the driver side head and seeing that the driver side valve cover has been leaking for quite sometime, could the two be related? After doing some research with VQ35/37 and valve cover leaks, I hypothesize that the main source of the leak is coming from the spark plug seal on cylinder #6. I'm going to find out in the following weeks once I work on the driver side valve cover and spark plugs, which is leaking pretty badly. Perhaps the spark plugs are fairly covered in oil causing some roughness, the couple of times the engine fired on 5 cylinders, and the lack of response.
Anyhow, I washed the intake plenum last night. It smells lemony. I also dipped the MAP sensor in warm soapy water to clean up the oil. It looks hermetically sealed, so I don't think there's much to worry.
To be continued with photos once I get to the cover and spark plugs...
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