Sounds like you guys haven't followed the Hero threads before. They too had light leakage and over time it resulted in dust under the screen.
It only stands to reason if the glass isn't sealed properly you'll be able to see that by the light leakage getting worse. Eventually, and the hero threads make it pretty clear, there will be dust under the screen.
Returned my first one, within the 30 days, for this problem. In the 30 days you can return it for any reason, or no reason, it's your option.
After 30 days, they you're dealing with a whole multitude of things. They may try to repair it, they may say you're full of bs, etc etc. They may just exchange it, who knows.
Good luck with it, but I'd point out, when trying to exchange, the hero had this problem and what the result was, and you don't want that... certainly worth a try imho.
happy 4th