FWIW, when I did an oil analysis on the identical vehicle (the 92 300D when it had 189,000 miles on it), the soot level was 0.8% after 7500 miles (mixed city and highway). So, in terms of soot, there should be no problem going AT LEAST 10,000 miles between oil changes with these engines. All the other trace elements were well within limits too.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 179k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 77k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife