So I have received my new grommet and PVC from one of the Buick vendors on this board, and it's very obvious "what's wrong with this picture" goes thru my head. You can clearly see that the old grommet is much bigger than what it should be, hence the PVC valve would go deeper and interfere with the valley pan. You can also see that with the correct grommet installed, the PVC valve barely goes past the grommet and will fit perfectly. Mystery solved!
