A W124 is a fine machine but your comment of "not working on it all the time" wouldnt fit well. they are still OLD.

the 96-99 W210 E300D with an OM606 is a fine machine. We have one and although I'd never part with my 300TD, I wouldnt mind having a second E300D.

The newer cars get you into the CDi and then the Blue tech. Both are fine autos. The CDi should be in your price range, but note that the newer cars might start to become big money to repair and maintain. Something to investigate.

If you consider a W210, dont buy it up near you. Rust is sadly a big issue with that chassis, right down to front spring perches failing. We went south for ours and picked up a super clean example with a turbo. 98-99 only federal W210s with turbo.

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85 300D 3 pedal. Current project.
83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.