Hey PJ,
First, make sure its coming from the rear of the block. Make sure that a leak at the front of the motor isn't running down the back, or the head gasket isn't leaking.
Barring that, its not good news. There may be one core plug at the back of the motor. If there is, I don't know how you'd get to it easily without pulling the motor. If one core plug is going, the others can't be too far behind.
good luck
chip
