The "locked up" compressor I replaced actually had a locked up clutch. The compressor pulley still turned free. Since that time I have replaced a couple more and neither of them even had an "x" on it. In regards to the wire connection the application manual for a 1981 300D shows you can use a Delphi compressor with the wire connection at the 3 o'clock position or the 6 o'clock position. I kinda like the 6 o'clock position better because of the close proximity of the connector to the frame when it is at the 3 o'clock position.

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Jim