Hi- assuming you are a US resident, you need to declare the watch on the customs form. Presumably you bought it in Europe tax free, and you will be billed for US import duty. As far as the strap, I only once imported a watch with a leather strap and it was indeed an issue, it needed a separate certificate and it took me ages. But this was a while ago so hopefully this has changed for the better, but I would certainly get my in line ahead of time.
