since mercedes is (and has been known) for its straight six engines I would consider one of these as a starter car. The w123 and w124 are great automobiles with relatively simple electronics (esp. the 80s models).

Just my .02

If you're stuck on the V8 I'd look at the SEC coupes (84? - 91), these are becoming collectors pieces and are some pretty nice 2-door cars. (I know you said 4-door, I just thought I'd throw this on the table since you say the car won't be used as a primary driver)

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE