I would have told the gun store owner to get me another brand new Glock from their distributor. Then you only have a couple days to wait.
With Glock Inc., it may take a good two weeks.
That's the fastest resolution.
Onto liability issues, unless you've got your law license and have practiced consumer law, STEP OFF TO THE CURB LAYMAN!
Sorry I couldn't resist power trippin!
From a legal perspsective, who touches the gun is very improtant. Ask any lawyer about product liability lawsuits. That's the maker's first defense, it was altered or modified by a user, distributor or someone down the supply chain. Read the disclaimers on your lawmower or some smokeless powder.
If the product was tampered with or altered, the law holds the tamperer responsible first. Then if the claim cannot be resolved by the tamperer, then the maker.
And so does your local Attorney General's Office.
I used to investigate and settle consumer protection complaints as an Ohio Assistant Attorny General.
Here, the product has been tampered with and having a mismatched or different box and a part that seems to be incorrectly installed or damages. Seems to qualify as tampering. Especially with Glock's know high QC.
The distributor and/or gun shop owner are first in line to fix the problem.
And Glock, the corp will make it right but I'd find out who the distibutor and dealer were and report them to Glock.
Never ever heard of such foolishness with a NIB gun. Once again, a pimp slap is in line!