Well, "infamous" being notorious, the big (usually dark) SEL sedans are and were infamous for being the transport of choice of third world dictators, potentates and kings.

In Africa, even children are sometimes named "Wabenzi"
When well kept, properly serviced with the correct fluids and parts, they are meant to last forever, and to be able to cruise safely and comfortably at their top speed all day long. They are built for the most part to be easy for the their mechanic to work on, and engineered to the highest standard, without regard to price point, and put together with great care. They are not cars built to be disposed of in a few years, and MB makes parts available, though not always cheaply. They will achieve star trek mileages and can protect their owners from injury in horrific crashes (Many or most of these these qualities apply also to your 240D, as you probably already know)
The very best diesel choice in America for them seems to be the '86-'87 300SDL, and I believe some would have to have their trap oxidizer worked out.
The 1981-85 300SD sedans are a good diesel choice too, with a few less refinements, being from an earlier year.
The gas models do ask for replacement of the timing chain, tensioners and guide rails about every 100,000 miles. A few remarks also can be found at
www.mbcoupes.com which covers the gas coupes and sedans, a quick introduction for buyers. The air conditioners on the W126 have been problematic, and door locking systems occasionally give problems, but generally the cars are not problems - unless they have been neglected, it can cost a lot of $$$ to catch up.
I am sure others can address the issues more comprehensively than this, but I think they are great cars.
Jim
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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...
1995 E 420, 170k "The Red Plum" (sold)
2015 BMW 535i xdrive awd
Stage 1 DINAN, 6k, <----364 hp
1967 Mercury Cougar, 49k
2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive

(sold)