My biggest rust concern on the W123 is when water leaks in at the windsheild gasket or battery tray, then quietly runs under the floor-mats and rots the floors under and behind the front seats, often extending up the sills to the seatbelt anchors. I've seen a couple of W123s where the lower outer seatbelt anchors were only attached to carpet!

Happy Motoring, Mark

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DrDKW