Stock rear spoiler removal question

[Pete_89T2]

My radio antenna crapped out, so to fix it by either a full replacement or by re-masting it (the motor works fine) will involve removing the stock rear spoiler.

Had no problem locating & removing the four 10mm nuts from underneath that fasten the spoiler's studs, but the two fasteners at the front edges of the wing (the ones covered by the little plastic caps) are another story.

Removing the caps and peering down into the hole, all I can see is a rusted blob that I assume was once a phillips head screw or a hex head fastener. I'm guessing this screw threads into one of those plastic grommets on the body side that are typically used for automotive trim pieces? Can someone verify what is supposed to be going on in there?

Sound like I'll need to carefully grind off those screw heads to remove the wing, and then most likely find replacement plastic body grommets and new screws to reinstall the wing.