My W124 in comparison is 95% rattle and squeak free. Only the visors tend to squeak, and it is quickly remedied (albeit temporarily) by lowering and raising them. But this W126 is just crazy squeaky!

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280