I hope your repair works. The closed space inside the cap will allow the CA off gas to do its bad deed, so leaving it open will help. So do not rush to close it back up.
Now, for the other part of the problem: your pen recipient. This person needs to hear that the pen is a "precision instrument", and to avoid being heavy handed with it. Also, if the pen is shown to someone else, they could redamage it by by unknowingly forcing it. That would happen in exactly the amount of time it takes to explain how the cap is removed/replaced. For some unknown reason, it seems that approximately half the world's population believes that one should really torque down the cap as it is replaced on the pen!
You might want to test your repair by tugging and tightening the cap a little beyond what you know to be "normal". Since the thread/cap assembly has failed once, giving it a good, convincing test before returning it to the customer might avoid having it come back again for the same complaint.