Ignition Module problems of the 1999 Saturn SL

Saturn was leaking oil into the radiator expansion tank and water in the oil. Over heating really bad that the car will shut down and not start until cool, and it boils over in the radiator expansion tank. October '03 had head gaskets replaced, and the heads sent off for service, one month later, its back to leaking oil in the coolant and water in the oil. Oxygen sensor went out, and has been replaced and so did the ignition modular, which has been replaced.