Well, my fitting is circular. So, vstech, it looks what you have is the perfect fit. What's your source?

However, the rectangular plug seems to fit snugly and securely into the circular hole. Think it's OK like that?

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 161k miles
06 E320 CDI "Rutherford", Black on Tan, 180k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 147k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 81k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife