I just thought about this, you said the bolt was tight to the floorpan, but how was the fit of the metal end piece to the bolt? It should be a little loose to allow the swivel action, but not so loose as to rattle.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.