The only experience I've had with a subaru and cooling ws about 8 years ago. Almost identical except it wasn't the head gasket, it was the head itself.
You should have done a complete diagnostic work up the very first time you encountered a problem. Running it after the first occurence, like I did years ago, just made it so much worse that the motor became worthless. At the time, subaru heads used and not even rebuilt were going for about $800 each.
Needless to say, the car went bye bye...