I had this same problem years ago on 'Rena 2.0'.

IIRC I just placed a bolt or large screwdriver next to the rear of the square captive nut
and used a tapered piece of scrap wood as a shim to wedge it in place.

This prevented the captive nut from turinng in its deformed cage and I was then able to them remove the bolt.

I replaced the mangled new captive nut holder with a used one from Pick*N-Pull.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022