I restored a threaded hole to the mount bracket for the left rear fastener for plastic underbody panel. And so am now able to hold up the rear outer corner of the left rear underbody panel. There's a little wheel strake there, if that's the right term for it.
IIRC, there are four M6 screws for each panel, plus a bunch of plastic push fasteners. The screws like to rust into their holes. Steel screw in aluminum threaded tube = nasty corrosion. Screw head twisted off, screw was corroded into aluminum threaded sleeve on back side of bracket.
This was the rear outer mount point on driver's side rear plastic panel. It goes into a bracket that feels springy. Turned out the bracket is held in with ONE bolt. Removed bracket. Found threaded sleeve on back side, to hold the panel mounting screw. Dremel + cutoff wheel removed a lip of the sleeve and then sleeve came out.
I epoxied a T-nut onto back side of the bracket, restoring the threaded sleeve right where it's supposed to be. I used JB-Quick. Tension when in use, is mostly in the correct direction, pulling the nut against the bracket - so it's not trying to come apart constantly. Dremel ground the plating off the nut's mating surface, and also smoothed the high spots off the bracket surface where the nut goes.
threaded t-nut with little holes for brads, or in my case, gooped epoxy
The nut I got was a bit longer than this one but I'm sure either length would work.