Just adding to this thread - W126 odometers have a habit of degrading the gears and failing to operate. Perhaps the odometer is a replacement unit, or perhaps the gears degraded and it simply didn't work for a while. If the car was dealer-serviced, their records will indicate the mileage discrepancy. Otherwise, take claimed miles on a W126 with a grain of salt.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)