All right, speaking of waterboxer head gasket jobs.
Anybody run into this :

2.1 engine, the outer rubber 'water gasket' on the left side started leaking
about two months after a full valve and head gasket job to both sides.

I measure how thick the water gasket is - it's 3.7 mm.
I measure what the gap is between the head and the block - I get the same
thing...3.7 to 3.8 mm ...in other words the rubber gasket wasn't being
compressed at all.

I figure I need half a mm less gap between the block and head, to compress
the rubber water gasket about that much, a half mm.

I measure the thickness of the metal rings that seal the head to the
barrels...they're 1 mm thick.
I dig around in my old gaskets and find new metal rings that are
....magically....just what I needed - one half mm thick.

It put it all back together.....using the same new-near rubber water gasket
cleaned up nicely, and my fav Toyota black silicone sealant.   'All fixed
now'
( And now I wonder about the other side of course - but it seems fine.,  The
van is at Burning Man now too. ) 
So anyone ever run into this before - that the metal sealing rings come in
two thicknesses....,
Or ??  
Thanx, Scott