But seriously folks....
If the unibody is rusted out where that big crossmemer-bolt screws into the frame-rail, it may be time to go body-shopping. I couldn't tell from the dark, blurry photo.
Most commonly, these rust out where the reinforcing brace that comes forward from that big bolt anchors with two smaller bolts at the base of the rear seat. It's not too hard to cut and fabricate a repair-plate for that corner of the floor. I just went through this on the right rear floor of my '84 Euro TD.

Happy Motoring, Mark

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DrDKW