Hi eric, so above I was describing about the duplicated surfaces.

Here I'll try to describe why this is not a clean intersection between these pieces.

So here's just 2 of the pieces:



So the problem is that although it looks at a glance to be a nice intersection, the area indicated here in red:



Is actually fairly complex - the pieces are at a slight angle to one another so they have a kind of slight criss-cross pattern (but only to a very shallow depth) in that area. If you select one you can kind of see how they actually intersect with that crossing pattern:



Because it is such a shallow intersection it is hard for the boolean code to figure out how to process that without having some little slivery bits left over, for example here I've booleaned just these 2 and you can see a slivery kind of result in that area:




Now multiple that many many more times and you can see that you're getting slivers upon slivers upon slivers... That makes for a kind of chaotic mess of slivery thin bits for the booleans to try and sort through and make sense of.

- Michael