I really didn’t want to say anything, because I was really hoping it wasn’t- but yeah. Head gaskets. I had to replace mine on my old legacy less than two months after I got the car.
Not too bad of a job, you do have to pull the motor though, as the DOHC heads are too tall to clear the rails when you try to jack just each side of the motor at a time… Check/replace the timing belt tensioner and/or the idler pulley as well.
Check with Fred at Capitaland in Scotia, he’s the OEM Subaru parts man (shameless plug).