I’m going to agree with Caddyman here. Subarus have been blowing head gaskets on and off since the early 70s.
Back then they used the wet sleeve engines and these would start leaking no matter what; and the recommended procedure was to retorque the head bolts every 15k miles. They would still blow.
In the late 70s things improved a bit. In the early 80s they started weeping oil from the 1.8 engines due to a head gasket redesign and only in some cases. Later on the situation became even worse.
What was the deciding factor? IMHO, it has to do with cylinder head torque. The early wet sleevers were beyond hope but in the late 70s the wet sleeve was done away with. Cylinder head bolts were retorqued at a 1000 miles just like the mechanical lifter, early 80s engines were. No problems with head gaskets.
Moving on into the future, cylinder head retorquing was eliminated on both the hydraulic and mechanical lifter engines and this is the cause of a lot of those problems IMHO. An aluminum block and aluminum head is going to have a lot of movement due to thermal expansion and no one can tell me that TTY head bolts are not going to change their properties.
Why did Subaru eliminate their head bolt retorquing recommendation? Because Subaru was paying for it at a 1000 miles instead of the customer and it’s another way of saving money.
Why else would Subaru recommend a head torque for years and then turn around and say it’s not needed on the identical same engine. Subaru at one time was saying retorque head bolts on a mechanical lifter engine but not on a hydraulic lifter engine. Same engine, same heads, same pushrods, same head bolts and head gaskets, etc. It makes zero sense.
OP, a head gasket problem is easy to verify with the tests I mentioned, assuming your problem is not fan or radiator related.