Do a search, this has come up many times in the past.

W126's have very specific rust out spots, bring a screw driver. Poke the frame rails if it goes through pass, poke the jack points, if they crush pass. Under the rear windows also rust out, lift the gasket and take a look.

Once the frame rails rot out, its ready for the crusher in my book.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200