I had this car for about 10 years and over that time period lots of things have gone wrong, I don't even remember the entire list. It's easier to list what hasn't been replaced: The 318 cid engine and the 3-speed transmission. These ran without breaking down. Although the engine was burning oil at 143K miles and smoking. It was worn out, but it ran.
Everyone who had one knows that rust is a major problem for 70's mopars. I had the trunk completely rust through in one spot. And where the tire went in the trunk, after every rainfall, I would get 3" of water in there. Also some rust over the dashboard, but hidden. After rain, water would leak inside the car, onto fuses, short something out and buzz. It would also leak onto my legs as I drove. I found this ridiculous, but didn't know how to fix it. The major place where almost every 74 Dart rusts is the rear quarter body panels. Even if you see no rust, it has probably been repaired. They all rust there (from my limited experience anyway).
Body panels had some misalignment. Like trunk didn't close perfectly. I heard it was common for 70's mopars. And the doors. It was much noisier inside than more modern cars.
It had a bad carb for most of the time I had it and only got about 14 mpg, combined with tranny with no overdrive. Once the carb was fixed, it got more like 16-17. Which is not much for a compact car. I carried a 5-gallon can of gas with me in case I ran out. So the whole car smelled like gas. I think refilled every 200 miles. City driving was abysmal, about 10. I did ran out of gas once or twice. Oh, and I should mention the gas gauge wasn't working right. I had to tell how much gas I had by the mileage. It didn't of course had a trip odometer.
It had some kind of annoying starting problem. A mechanic fixed, but I didn't know what it was. Ignition switch maybe.
The trunk had absurdly little space in it. You couldn't put anything in it. And it leaked badly as I already said.
AC never worked in it. The first year I had it, the car was overheating and we had AC disconnected. Although I don't know what exactly it was.
One good thing about it, it was relatively easy to work on. Spark plugs are not hard to swap. Some other things are easy. I replaced the water pump on it myself. As well as the fuel pump and filter. The radiator was replaced, but not by myself. This is the most redeeming feature of the car, you can basically service it yourself - and you will need it.
These older cars have to be in great shape to be usable. If it's neglected, like mine was, it will give lots of problems. Mine used to stall in rainy weather, and lose power steering, and power brakes. One time it stalled when I was coming down a steep hill, that was just wonderful without any power. Carburetors were a love/hate relationship for me. They were easy to service without all these sensors, but were not as efficient as fuel injection and ultimately more problematic.
At the end of the decade I had it, every few weeks something would fail on it with regularity. The door locks (by that time I never bothered to replace them), speedometer, then speedometer cable (not even mechanics could fix that one, and sometimes it would just die when driving) Several alternators.
I turned this car into a total beater, with peeling paint all over the body, and rust. I hit and replaced one of the front side panels and painted it the wrong color. This has nothing to do with car's reliability, but in its final years with me, it looked like a total beater and I stopped worrying about its appearance.
One huge problem was, it went through many tires. The front end had trouble staying aligned or something like that. I would fix something on it every month and finally it needed even more repairs, like a total front end rebuild and I just gave up on it and sold it for next to nothing.
Because it was RWD, it was very unstable in snow and rain. The rear end was very light. Even 2" of snow could mean it getting stuck. I once almost got into an accident because of that. Hit the brakes and the car turned 180 degrees, onto the oncoming lane. But even then I prefer RWD.
It's V8 engine (318 cid or 5.2L) was realiable. Like slant six. But it was worn out with somewhat more than 100,000 miles on it. Today they build these engines better. Also it was pretty weak. It sometimes struggled uphill. I found that absurd given how light the car was and the mileage it got. (I got a small block Chevy after that with a 350 V8 and it had much more power, much better mileage and was much heavier.) I don't know if that was because the old 318 had bad compression. But in the 70's both 318 and slant six were pretty weak engines with high gas consumption.
I think I would consider owning another one, but with lower miles and one which has been garaged. Even in that case, these cars are high maintainance, and really not as good as newer V8 vehicles. They don't cost very much on the market. These cars are 30 years old and stuff rotts on them, wears out, rusts, etc. I got fed up with endless problems in my Dart when it had only 147K, but it looked like it had half a million miles. Age killed it more than miles.
I think one thing that's better than 70's mopars are early 80's mopars. By that time, they learned how to properly galvanize the body metal and I saw far less rust on early 80's sedans.
Keep in mind parts are getting harder to find than they were 10 years ago.
After about '72, emissions killed all the power in the 318 engine. The one I had had only 145 horses. Prior to that, I think it was more like 200 hp (?). So it was a weak compact car which had terrible mileage. It didn't have a very good horsepower to weight ratio.
I did like my Dart, but it was one of these stupid "first car" things. I will probably always remember good and bad things which happened to me when I had it, and what I did with it, where I went, these sentimental reasons. I am also glad I learned a lot about automotive things on it. I think way cooler vehicles are bigger mopars, full size with either 318 or 360 or 383 engines.