what i did on my 84 300sd is i swapped the pass. and driver side since when u unlock the driver side all the locks unlock. you basically take out the hadel on one side and swap it with the other. thsi was on a w126 so i don't know if it applies to all models.

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198? 300D ???K - Future DD
1989 300TE 285K - traded in '12
1984 300SD 186K - Sold in 08
1978 300SD 330K - Died in 05