The SUBARU BOXER engine is itself a study in symmetry. Yes, other types of engines have to have a certain amount of balance or they’d shake themselves apart. However, the horizontally opposed layout of a Subaru engine has inherent advantages.
With cylinders directly opposite one another, piston movement is in a line all the way across. Power is distributed evenly on either side of the crankshaft.
In an in-line engine, all the cylinders are laid out on only one side of the crankshaft. Power drives against it from only one direction.
V-type engines have cylinders connected to the crankshaft from both sides of the V. However, instead of having the balance of direct opposition, piston movement in either bank tends to push the crankshaft off-center.
Well this is what i saw that made me believe boxers are supposed to be more reliable. though i will admit it came from a subaru web site so im not sure how biased it is. As you said though youve never blown a motor but have had trouble with head gaskets and we all know that old subarus along with most other old import cars werent famous for great head gaskets