It’s true that disease is in many cases a sign of genetic weakness. The decision to breed or not to breed can be subjective, depending on the circumstances. For instance, is this the only bird you have to work with, or are the others to fall back on. Sometimes you have no choice. But when possible, I always breed to the health and cull the sick.
Now, as for sour crop, my experience is that treatment is rarely effective, and when it does work, it usually returns in the future. If you find it necessary to breed this bird, make sure to be very selective of the offspring. Any sick birds must be culled.