ok, the head gasket failed beacuse of a dual thermostat problem that nissan recognized in a tsb. one thermostat opened at a different temperature than the other and caused problems circulating the coolant. the second thermostat has been removed per the tsb. the motor was replaced due to cost. they found a used motor for a good price and installed it instead of rebuilding the old motor since it calls for the motor to be removed for rebuilding anyways.