It could be all the things you mentioned but most likely it is the oil pressure switch located just above the oil filter. And it is the first place to start as it is the chespest other then oil which you already checked. O'Rielly/Kragen has them for about $6.00. The blinking is caused by a electronic timer which is supposed to get your attention over just a steady light. What fails in the sensor is the seal between the switch and the oil port. It allows oil to leak into the switch side so the switch diaphram cannot move away from its grounding point.