Well it's only metal, get out the hole saw... I know he doesn't want to hack this car up.You can’t double nut this. This is the access…he can barely get the square nut back in there…
Holding a broken captive nut
On my 1991 mb 350sd I can tell the guide rod mount is loose. So I’m going to replace it, the bushings, and the lower control arm bushing. Everything went well until the captive nut on one of the main bushings broke. There is very little corrosion but apparently enough on this bolt to cause an...bobistheoilguy.com
But for a beater, a significant percentage of the unit body isn't really doing much and could have a hole in it without consequences, but you have to do an educated guess where...
Now that I think about it, if there's space, adding some washers or a larger nut as a spacer, at the bolt head end can get the captive nut onto clean threads of the bolt.