Again, what happens to O2 /AFR readings if the rings are not seated yet or some such and some oil gets into the combustion chamber?
Have you tryed moving the O2 sensors side to side.
Here is a picture guide to reading spark plugs:
Spark Plugs
I am not an expert but it dose not look like there is a lean condition
Also could be an ignition issue and the plugs are not getting hot enough:
"Dry and Wet Fouling:
Although there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. If the insulation resistance drops to 0 ohms, the firing end is fouled by either wet or dry carbon."