They both sound like nice cars. "Value" is so subjective. OF course the diesel will return better mileage, and it's an economy car. Theother one will drink more gas but you will have an airbag, abs, a more hefty and comfortable car for a commute, that would probably be safer in a bad accident, if the worst happened.
There is some value there obviously....
On the flip side it has more gadgets and accessories that coud go wrong and cost more to fix.. Im guessing but the 240 D probably cost about $35000 when new and the '90 420SEL cost about $55,000 when new.
Each would last a long time, but if either one seems neglected, it could have thousands in repairs. For ecample, if one had a non working air conditioner, a notorious fault in thes cars, it could cost a lot to make right. Or if it needed a timing chain soon, or lots of suspension work, or you discovered rot, rust or leaks on the car. Body work gets expensive and body integrity is good to have.
If both check out in good conditions, with a paper trail of service history, which would you rather drive? The easier on fuel 240, easier to fix, simpler 240 with very modest about 67HP, and have to shift yourself, a p ain in heavy traffic. Or the larger more coomfortable, thirstier and possiblely more complicated luxury one?
Drive both and see which one you would rather commute in. Either might work for you
Perhaps driving each would help. Then check the buyers guide for the W123, and getsome more tips for the 420 by looking at the buyers guide for the W126 coupes, some of it appies to the 420 SEL.Welcome to MB Coupes!