The two that I have replaced were on a 124 and a 210. I do not remember one end being different from the other. Do they look the same? If so they were probably just marked a certain way during manufacturing for some comunication purpose.

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1996 (W210) E300D 86K - Traded in for a Lexus
1992 (W124) 300D 2.5 Turbo 202K - Sold
1983 (W123) 300D, 146K - Sold
1970 280S, 263K - Sold - Beginning of addiction