My guess would be that the oil pressure sensor (i.e. fuel pump switch), if defective, may fail not only intermittantly, but could drop from the normal 12 volts to something less, thus causing relay chatter. The relay chatter is caused when the pick voltage is less than needed. The theory behind relays is that it takes more to pick a relay than hold the relay closed.
This is classic failure, imho.
The reason many mechanics and dealers fail to find this type of failure is that they are weak in the electrical skills necessary to troubleshoot electrical/electronic problems. Their skills are strong mechanically, but not in electrical theory (i.e. trace a ladder diagram, understand loop and nodal analysis to isolate a complex circuit loop, etc.).
Nova Rod