This is a very interesting paper.

The most important innovation got one sentence.  The access ports allow the
pistons to be installed after the block is assembled.  This means no
assembly joint between the block and cylinders.  Every other boxer engine I
have seen has a joint between block and cylinders.

This one little innovation is the key to the Subaru engine.  It allows a
monolytic block and requires slipper pistons.  Fewer assembly joints means
fewer leaks.  Lower parts count and ease of assembly means lower sale price.

BTW my wife Beve is down in Central Florida this weekend in our brown 85 Westy.

Ron

near Great Smokey Mountain National Park in East Tennessee

84 Westy
85 Westy