I have the same issue, There are two ways to fix this.
A. get a new or used nut and replace
B. use a "nutsert" and a common threaded GRADE 8+ bolt.
either way, the seat needs to be removed, but B is a substitute for not finding nut in plan A.

I have a parts car so I can just go rob on of of it.

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RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

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