I have a 2011 suabru outback with the SOHC 2.5 4 cylinder ej25 with no turbo. Had head gaskets replaced recently was fine then stated to burn about a half quart of oil every 500 miles. Head gaskets are not the I since I am not loosening coolant. I have heard there have been issues with this generation of ej25 engines with the piston rings allowing oil to pass into the combustion chamber.
How many miles on the engine? How long after the head gasket job did the problem start?
Subaru has had oil burning problems on some models and there was even a class-action lawsuit, but that year Outback doesn't seem to be listed among the affected models. (Supposedly it's the 2013-2014 Outbacks.) About the only easy/cheap thing you can check is the PCV valve. See if it's allowing oil to be sucked into the intake.
Also check for oil drips, it doesn't take a huge leak to lose a quart in 1000 miles. Is there oil residue in your tailpipe? On the spark plugs?
My vote is for the PCV valve, which most people seem to ignore at each oil change. How about a compression test just to be sure?
