One problem related to coolant leaking has been reported for the 2004 Subaru Outback. The most recently reported issues are listed below.
Blown headgasket at only 40k. Car has been maintained on a regular schedule with extra care car when needed. Took to dealer and complained of smell of coolant in the interior of car when driving and after shutting vehicle down or at a traffic light stop. Took to dealer complaining of a noise coming from the bottom of engine. After the dealer examined vehicle nothing was found as per report. I took the car for brake repair and the mechanic noted a coolant leak from the left bank of the engine block. He stated that he car has a blown headgasket on the left bank of the cylinder block. The warranty on the powertrain is about to run out and he advised to return the vehicle to the dealer for the repair. He did state that the dealer will only repair the bank that is leaking and the other would not be covered and should be done at the same time to prevent the other bank from blowing out due to a change in the balance of pressure on the block resulting from the replacement of only one headgasket.