Look here for plug readings [link]http://www.prme.nl/forum/viewtopic.php?t=10[/link]

Specs on the fuselage is not a mixture indicator. Look down into the plug where isolator meets plug body. If you see a black ring, the mixture is OK.
The black plug body is indicating a slightly rich mixture. Oil has little to do with that.

Placing the sensor on the front of the engine gives low temperatures. The prop turbulence forces the cool air deep into the finning. They should be placed at the rear, where the sensor is not cooled by the airflow. That is the main reason for the massive temperature rise after stopping the engine.