Is it normal to have a light brown half moon on the exhaust side of the piston? I am assuming that the brown is a sign of blow by. I have good comp readings of 210. The plug looked funny on the screw on top....it was pitted:think anybody seen one pitted before?
The discoloration of the piston is normal, it is caused by the piston being exposed to the exiting exhaust gases during the exhaust phase. The pitting on the connection end of the plug you describe is just corrosion from moisture, don't worry about it.