AMC V-8 heads are known to crack at the lower front and rear corners if not torqued correctly. There's a sharp point in the casting. Between cylinders has to be a gasket problem. I doubt a few heat cycles will do anything. It might take a re-torque of the head bolts to proper torque in the proper sequence. If that doesn't fix it, you'd have to remove the head to find the failure. I've had good results with the AC-Delco stop leak tablets, but I only use them as a last resort.
Bob
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