This is correct, internet diagnosis is one big crap shoot.However there are some basics to check first, and hooking up a good scan tool would have been easier than pulling a spark plug,and would have told him he had a bad O2 voltage and which one. But who knows, this may not even be his problem,but just one of his problems, there may be others. And FYI he did state that he did not feel the O2 was bad cause he had no SES light,which to me is odd unless TS takes the ability for the ECU to recognize engine codes, out of it during their flash.
I am in no way getting into a pissing contest with you, and not saying who was right or wrong,Im simply pointing out that most of the time, the problem is the most obvious thing right in front of you and you dont see it..
If it were me, as soon as he said he was 12.1 at cruise in closed loop, I would immidiately check the O2's and the MAF first, then make my way to the plugs, but remember, the plugs are only an effect of a cause. Tracing down the cause of a fouled plug is the trick.

 

That's because the "gasket" is built into the acutal valve cover (believe me, I tried ). You can't get them seperate. A new valve cover gasket will do nothing for you unless your are actually leaking oil from the area between your valve cover and your head.

Good luck....

 

The last time I checked Technosquare does not have the ability to tell the ECU to disregard or not throw a CEL if a DTC is detected. I also find it odd he did not throw a code though.. disturbed which O2 is burnt? Primary or secondary? Maybe I missed this and he already posted this..