The numbers like W123 and W140 refer to body designs. The higher the number the more recent. Within these bodies, Mercedes made various models by putting in different engines, and more or less luxurious interior appointments and features. The model numbers refer to the engine size in litres. For example the 300 would be a 3 litre or 3000cc engine, the 190 would be a 1.9 litre or 1900cc and so on.

The D suffix means Diesel. E means Einspritz (fuel injection) and is seen only on older gas models. S means Supercharged or Turbocharged. C means Coupe or in other words, a 2 door hardtop body style. L means Lang or long wheelbase.

So if you had a 300SDL it would mean, a 3 litre Turbocharged Diesel car with the stretched 4 door body.

I would suggest that you buy the newest, best condition car you can afford. Ask to see the service history and past repair bills. A car that has been serviced regularly by a Mercedes dealer is likely to be much more trouble free and cheaper to own in the long run than one that has been neglected.

These cars are durable and long lived if maintained by the book but can be a nightmare if let go. When I say maintained by the book, I mean the official Mercedes service schedule as in the owner's manual or service manual.

Buy a good car and maintain it by the book (you can do most of it yourself) and the car will last so long you will be sick of it before you ever wear it out.