I like the cars feel, suspension and visibility while driving...
If you like this era and vibe of vehicle, and want a diesel, try to find an early '80s Volvo 240 diesel or 740/760 turbodiesel. Better cars, cheaper to buy and own, much nicer to drive. They share the same feeling of lots of glass, great visibility, tight turning radius, nice seats and space in the interior, classic looks, etc. But they don't have 45-year-old vacuum hoses running throughout the car, the suspension and brake systems are simpler and much more robust, parts cost much less, etc. And at least in the case of the 700 series, the entire climate control system is a GM design meaning it works great, is reliable, and is cheap and easy to maintain. The opposite of the Benz situation.
If all else were equal I would also suggest looking for a BMW 524td or Peugeot 505 TD or 604 TD. Both are also far superior vehicles to the Mercedes to drive/maintain/own (my personal opinion at least) in terms of expensive European diesel sedans from that era. BUT all else is not equal -- the BMW and Peugeot cars are very limited in existence and parts/tools/knowledge for them are if anything even harder to find. Pain to own something where that is the case, even if you did find a car in decent shape. That is really the only major advantage to the Benz diesels -- there are still so many around, and parts/resources are plentiful.
But the Volvos do have that same advantage. Still tons of gasser Volvos on the road so body and chassis parts are everywhere, plus Volvo still supports the '80s cars quite well at the dealer level. The diesel engine in the Volvos is not as common but it has the advantage of sharing almost every part in the engine (except for the block, head, camshaft, crankshaft, and a few gaskets specific to those parts) with any number of other VW/Audi diesel and gas engines. So most everything you need to keep one going is readily available and cheap.
There's my sales pitch, having dealt with many examples of all of these back in the day (yep even the BMWs and Pugs, and other oddballs)