W124 front seat track bolts missing threaded body nut.
 

I am swapping front seats on a W124 and went smoothly without issues....pretty easy. But as luck would have it the last bolt to install was the rear outside one on the drives seat and the threaded nut in the body the bolt screws into is GONE !!! Obviously a captive nut...does anyone know how to access the underside of the floor that supports the seat track? It is not accessible from below...there isn't even a grommet to remove to access the nut. There must be another way...unless they installed it in the sub-floor then welded the whole thing to the outer shell. I don't believe Mercedes, back then in 92, did things that way.
Any help so I don't start ripping the interior apart unnecessarily.
Does anyone have the diagram of the assembly.

If there is an additional cover welded to the bottom of the floor panel there (no diagrams handy), you could locate the spot by hammering a punch from above, then cut a hole from below. Repaint and close with grommet if possible.

Yeah..but not really the preferred solution. There must be access somewhere.

Same thing happened to me! No solution yet.......

I figured it out.....remove the seat and lift the carpet...bit of a pain in the A**..but it will expose the slot that the captive bolt slides into. Pretty easy once the carpet is lifted. I think I am going to just cut the carpet under the metal support the seat leg rests on, the piece the bolt goes through, and thereby exposing the sliding bolt and just slide a new one in. Simple....and the cut won't even be visible.