I know this is a long shot, but since it happened to me, it could happen to anyone. When installing my intake, the thin section of gasket seperating the #1 & 3 intake ports slipped. It slipped enough to cause the #3 side to draw in oil. Not enough to burn smoke, but enough to lose about a 1 quart per week. Note: the gasket in the picture was torn when removing the intake.
Check your plugs for signs of fouling. If you find only one, this could be your problem. Good luck, Ed.