one reason to change the oil regularly is the moisture that builds up in the oil, especially if the engine does a lot of short drives and doesn't get fully heated up to boil that stuff off.

If you like your MB engine, never just change the filter - good to get that sooty oil out.

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1985 300TD 1981 Scirocco 1.6D conv 1986 Golf 1.6D 2003 Golf TDI