well i used to be a roofer,( the foreman, not a pee on) so i know a thing or 2 about water proofing, and from 20 years of roofing i know what materials would work well in what situation.
a old bike tube, and rubber cement are things that a lot of people have on hand, just sitting in a closet. and a tube of caulk just sitting there from other household projects.
and, because at the end of the day it only cost me 15 minutes of my time, and no parts to buy, and it still works. for me any ways. and my floor was soaked a bunch of time before i got to fixing it. bone dry now for over a year. and im using a bag lol ( i totally thought i'd be shopping for that part weeks after i did this, why fix what aint broken?)
i do see how that new dealer cowl hooks under, and just lets the water go by with out bucking water on a seam, and that should by all means work, but if you got a torn up flap, my way works on the cheap.