Kind of confusing. Are you saying that your car didn't have the 3rd seat option? The third seat doesn't bolt in - it just lays flat and is locked in with a couple of clips on the floor where the backing is stored. The backing for the seat is another piece that pops up from the floor of the rear cargo area. The seat belts are attached to the side pillars of the cargo area too. Sorry I don't have any pictures.

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles