300SDLs are great. The handling also seems a lot stiffer than a W123 ( i haven't driven a 300SD). If you have the money go for the 300SDL, its a lot more enjoyable than the OM617. That it as long as you do a lot of highway driving. The 617 feels torquier and peppier around town. The 603 really shines when you can take it out and open it up.

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1985 CA 300D Turbo , 213K mi