My father bought this car in 1998 with less than 100000km and in museum condition. I was young and resented trading in our more modern 190E for a car designed in the 70's, but I have since come to love my "beast". The W123 is a magnificent piece of engineering. The styling is classic and distinctive. Living and working in a large city obsessed with new, the 20 year old Benz stands out. With care, it is a better car at 20 years old than many new cars today, which is a testament to how far ahead Mercedes was in that era. Non-car people often mistake it for new.
The Diesel is incredibly economical though obviously louder and a bit slower than one would like. Nevertheless, the engine sounds almost like a growling V8 and is satisfying. As for acceleration, the engine produces "thrust" rather than power. You do not have the response off the line of a modern gas engine, but once the turbo engages the engine will pull forcefully. The throttle has a very active response, unlike in a modern gas. The engine runs at peak torque at 100kn/h, so when you hit the accelerator at that speed the engine instantly responds and will pull over 170km/h. Because of the high compression of the diesel, releasing the throttle has the same effect: the car slows and will hold speed down steep hills without breaking. But the real performance of this car must be gauged differently. I have had the car loaded down, with extra cargo strapped onto the stuffed trunk without ever bottoming out the suspension, driven 150kn/h with the air condition on and gotten 28mpg.
This car looks like a car should look. It drives like a car should drive. There is no nonsense here: No leather seats (I would be replacing leather now, but my MB leather looks brand new), no computers, no ABS, and no air bags. Yet I would take my car against an SUV any day.
As you can see, many parts have been replaced and maintenance is expensive, but I haven't yet found a reason to trade in this car. W123 drivers are nearly fanatical in their devotion, and I feel much the same. If I were to buy a new car, it would probably be an OLDER Mercedes: a 6.9 as a toy, perhaps. The reason is simple: when you look up the word car in the dictionary, there is a picture of a Mercedes from the late 70's.