My info lists '67 as the last year for the M189, aluminum six, based on the '50s 300 engine design. Acording to that, by '68, the M130 2.8 replaced the 300SE six as well as the 250SE (now rebadged 280SE) But check the VIN and engine as some of these cars have been titled with the wrong year.

Happy Motoring, Mark

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DrDKW