I too had a cracked bass that was repaired by Alembic. The crack started under the rear battery cover and went to the core and up to where your arm would rest on the top of the body. This crack was BIG. They repaired it and no one knew it was there but me. The crack was repaired in 1978 and when I sold the bass 2 years ago, it still looked good. They did a great job on this.
If you like the bass, I would not be concerned about the crack back there. I have an Alembic bass that I bought a long time ago with a cracked headstock where it meets the neck. The crack is still there, never been repaired, and I just love the bass. One of these days I will have them fix it, but I am enjoying it too much.