I bought a cheap solid wood ukulele and discovered a crack in the back. It is smooth at the outside, but visible at the inside and when you hold it against a light source (see pics). I am wondering about filling the inside gap with some glue, but brought it to the local luthier to get an opinion or repair estimate. He said that this was a weakness in the wood texture which was superglued before they even assembled the uke, and would not require and work to be done. But I am concerned that this may be a point of weakness and still consider doing something. So if I put some additional superglue in the crack, is there a risk that the already existing fill could be dissolved or weakened? Or should I try another substance, e.g. I have some regular water soluble carpenters glue around?

Also I think the action is a bit high and I asked for a replacement saddle to work on. But he said his saddles were too thick, so if you can recommend a source to buy a cheap ukulele saddle please let me know. Thanks.