Looking for permanent replacement for pullover

as much as I want to, I cannot do pullovers anymore, my left shoulder buckles after 45 degrees. I can do any other excercise using my left arm it's just this single movement that gets me. I wonder do others have similar problems with this movement or any other movement and importantly is there an excercise that I can substitute each time it appears that will work the same muscle adequately.

Any suggestion appreciated, thanks