I only borrowed my grandmother's car once for a long weekend, but it got 29 MPG with 70% city driving. The car is technically more complicated than a W123, but I think more mechanics would know what to do with it. It probably isn't a whole lot faster than my 300D turbo, but it sure is smoother. I'm not saying that you should get a Corolla, it was just an example. If I were going to get a car like that, I'd probably go with a Honda. More efficient, more fun to drive, better economy, better reliability (probably). Good luck.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside