Ok, I would continue with a thorough cleaning of the pipe. There’s great threads on the pipe maintenance section of the form. I would carefully clean the Mortis area of the pipe. I can’t tell from the picture if that is carbon residue and gunk from years of not being cleaned or if it is glue residue indeed? Once that area of the pipe is thoroughly cleaned, You could try refitting the horn midsection and see if it seats well and doesn’t turn?
If you can get the midsection and stem to properly connected to the pipe and considering that the cracks don’t go all the way through, I would say you’re ready to smoke the pipe. It’s definitely a pipe you want to smoke slow and low. Any excess heat could exacerbate the cracks in the pipe.
I was hoping that some of the pipe restoration exports on the forum would have chimed in by now. Hope this helps. Whatever you do, let us know; I’m interested in the outcome!