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, 156k miles
06 E320 CDI "Rutherford", Black on Tan, 173k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 143k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 67k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife