If you were to retake a 3rd time, anything less than say, a 520, probably will not be in your favor. Your score going down is definitely not a good thing- schools view MCAT scores in confidence intervals, where if you score a 514, your "true" score might be anywhere from 510-518. Scoring a 509 on the retake tells schools your "true" score is on the lower side.
I would recommend against a third retake.
Kevin W, MCAT Tutor
Med School Tutors