dablk1, although I have never removed a 124 rear armrest I suspect you need to remove the seat back on both sides to access the mounting hardware for the armrest. So remove the 1-piece seat cushion which will expose the bolt that secures each seat back. Remove that bolt then lift up to remove each seat back. Once both seat backs are removed the remainder of the job should be self-explanatory.

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Fred Hoelzle