In short, the answer is your lower must be damaged beyond repair due to a complete weapon failure. I.E. my gun blew up in my hands damn it!
Colt doesnt like the idea (nor would any manufacturer) that you have potential civil action against them. The plain and short of it is they will obligate themelves to do a remanufacture if they suspect a defective weapon. But you will wait along time for your remanufacture. 18 mos or longer. Alot can happen in that time frame.
BTW you dont threaten them. You make enquiries of why did my perfectly functioning weapon go boom? Ask to speak to their legal department if you are getting nothing from customer services.
It can work. Its been done before.