This old dear has dried out. I sometimes think I know how he feels. The centre joint on the back has opened up completely- and that is a tricky repair in itself to do nicely because the curved surfaces are so thin- but it has dried out and warped in the process. Wood changes shape and size with moisture changes, so the pieces no longer fit the perfect book-matched joint that the maker cut with a jointer plane.
What I've done in the picture is pre-clamp the pieces while I undertake preliminary rehydrating of the wood, prior to gluing. If this doesn't make the joint disappear, the back will have to come off and be re-joined.