Klima relay is a common AC failure point on the 85's.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

The car sounds to me like it deserves a closer look.
If the interior is sound, except for that leaning seat, that's big plus. Why is the seat leaning or busted?
If there is no major rust in the body or dents - another big plus.
Also, the engine is low mileage - if indeed the odo is working?
I'm thinking no more than $1000 based on your initial description. You could prolly get it for $500 maybe less.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

The passenger seat is busted because an enormously fat woman with a steel hip rode in it all the time.

There's no major rust (as compared to my 220D) and there's only 1 small ding.

The odometer works.

"The passenger seat is busted because an enormously fat woman with a steel hip rode in it all the time."

... sounds like one of those sinister characters from an old James Bond movie...

... hmmm... might want to check driver to passenger (left/right) ride height. And passenger door/hinge operation/alignment if it's that bad - some folks like to hang on them to get in and out...

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1987 300SDL
2005 Ford Excursion 6.0L Powerstroke, 6" suspension lift

Ok. So where does that leave me?

It leaves you with a wife that does not support this project. Be verrrrrry verrrrrry careful. Thanks

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83 300D 227,xxx miles, sold
86 300 SDL 130,000 miles, sold