Hi Steve - attached here is what I mean by moving your object a little bit over so they push through each other.

If you look at this one, the side object is sunk down a little ways into the main body instead of just skimming right along its surface.

Now you can use boolean union with it as you were trying to do originally.

It's easier for the booleans if you make pieces push through each other a little bit like this rather than making pieces that barely touch.

- Michael