I am currently feeling exactly like you felt with the old bummy seat and I'm exploring my options to increase comfort. To further complicate matters on mine, I have the w123 coupe with its specific seat bottoms.

Something is got to give and SOON!! My back is killing me today and I'm sure it's from the seat.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"