So today thanks to this freakin cali weather that can't seem to wanna make up its mind i finally had sunshine and time to tear out my rear interior and diagnose the trunk leak thats been plaguing me since i picked up my hatch a few months back.
Well the good news is that it wasn't too severe; just the notorious tail light gaskets we all love. I'm contemplating making my own. But also theres this curious hole below the passenger tail light that water is leaking through from behind... is there a missing grommet that's supposed to go here?

 

Yes if im not mistaken it is the wiring for your license plate lights. So to answer your question yes it is a water proof grommet.