Those 13mm nuts on the connector pipe are hard to work in that confined space. I dropped the lower aft one and heard it hit the street. Reaching under the car to get the dropped nut, I found a small puddle of black engine oil covering 2"x1.5" roughly parallel to the back of the engine. I jacked up the driver's side and crawled under to look for the source. It is coming from the #6 cylinder at the exhaust manifold.

Sixto, This oil drip is new to the car, and the puddle appeared after the short time that the car was idling to test the fuel delivery to each cylinder. I'll stop trying to remove the exhaust connector, as this engine oil dripping from the rear-most cylinder area may redirect your guidance.