Hey there old friend, hope all is well! I have rarely seen Acidified Copper Sulfate mentioned for sour crop on here and I got that advice so many years back from Carla (Allen Wranch). If I have a case that seems dire, I do use mine. Can't hurt, might help. It is used to kill algae in drinking...
Sorry I'm late to the party but you're getting experienced advice. I see crop issues in some when they are heading toward their end, but remember that more often than not, crop issues are a symptom of something wrong in the body, the first outward clue something is going on inside. Shell-less...