Out of warranty? I'm not sure what you can do.
You looked like you have the knowledge to unlock and relock the siding. I was just suggesting, if so, that you unlock 1 piece below window and see if there is leak evidence. If so, and builder is involved in fixing the one you first posted about, he is showing that he is concerned and may address any other issues.
I'm just a dumb roofer/remodeler, so I don't know much about legal stuff. But I think there is 'an implied' liability' statute involved here. You would need to consult with a lawyer to see if there is any recourse. There may be none. But if there is a problem, you or the builder would be able to address it more efficiently now, than after major damage has occurred.