Hi Michael, so in your case it looks like you would need to use the scale down + join + scale back up case to get it to join well.

There are a couple of things like that extending spot I showed earlier that are not ready to join, but other than that these parts here can be joined:



There is a little slivery hole right here though where there seems to be a missing surface:




But anyway, I've attached the results after joining, and also an OBJ file that was created from the joined result, you should be able to see now that there aren't any cracks in the mesh anymore (aside from that sliver above).

- Michael