Any update on this part number?

Go to Amazon and search for this

Zerostart 3600001 Auto and Light Truck Replacement Cordset for Freeze Plug, Engine Block, Oil Pan, and Transmission Heaters, 5-Feet | CSA Approved | 120 Volts

Napa had these available IIRC. $20, and it comes with the threaded collar.

Edit: https://www.napaonline.com/en/p/KAT28216
Napa part number KAT28216

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Milan Brown 1979 240D, rebuilt OM617.952 turbo diesel, rebuilt 722.315 transmission - engine spun a rod bearing

1979 300SD, ~90k original miles, all stock

Those look to be $2 more money and looking at the photo of the connection end it doesn't look like it would fit . It looks to be more round than rectangular.

Have you purchased one of these and actually put it on a w123?

Thanks,

Pete