That spot was the "aft field joint" according to wikipedia. According to the diagram linked[1] that is distinct from the case-to-nozzle joint. [1] https://scie

That spot was the "aft field joint" according to wikipedia. According to the diagram linked[1] that is distinct from the case-to-nozzle joint. [1] https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts_asm.html#srb_mod_compare https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/...