If you have to have a W124 wagon and don't want to get raped just find a 300TE. The M103 is a fine engine. Unless you drive a lot fuel mileage is a wash.

You can probably find an 89-91 with 100k miles on it for the same money they are asking for the older diesel version.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200