We talked to another couple who had a 23 with a shower surround that developed a crack. They said the dealer installed an upgraded version of the surround to repair the problem. That is not the same shower, but may have a flaw in the mfg. Certainly would discuss with either responsive dealer or JC.
A boat would be repaired by grinding out the crack, laying in new glass, and finishing off with new gelcoat. Our dealer says they do not have fibreglass repair capability and suggest using a boat repair company. Since ours is only scratched, we have not investigated.
A small crack might be resolved by stopping the growth with a small hole and filling the crack with an appropriate caulk, but I'd consult an expert first.
Hope you find a solution. Pat