Representing a gigantic step forward over the four-cylinder 190SL, the six-cylinder 230SL appeared in the early '60s as a dramatic styling statement that still is striking today. This supurbly built car with decent-but-not-shattering performance remains quite affordable, with usable examples starting at $15,000, nice cars at $20,000 to $25,000, and first rate examples going for $30,000.
The 230 (1963-66, 19,831 built) and 250 (1966-68, 5,196 built) are a bit less valuable than the more numerous 280SL (1968-71, 23,885 built). Body changes are minimal, but the hubcaps and trim rings on the 230 and 250 cars are separate pieces; the 280 has a single large cap. Alloy wheels were not generally original equipment.
Rust is an issue with the basic structure of the car, although the hood, trunk, doors and tonneau were made of aluminum, which was rather exotic for a production car. Look carefully at shut lines for the hood, as these are difficult to restore to the original build standards. There should be a small crease on the outer fender at the headlight rim. If that's missing, it's an indication that the Bondo bandit has struck again. The dash should be painted body color, but hardtops often are a contrasting color. Standard equipment did not include two tops, except on the 1971 280SL.
The engines are typically M-B robust. The front crankshaft seal is the only probable source of leaks. Oil pressure at idle when warm may seem low, but should peg the abbreviated oil pressure gauge from 2,000 RPM up. Horsepower increased with each successive model (150, 160, 170), but the real changes are in torque, which increased 10 percent in the 250 and an additional 10 percent in the 280. All cars had Bosch mechanical fuel injection, which must be set up by a professional. Once adjusted, the injection will be trouble-free as long as the car is regularly driven.
The Mercedes-Benz Club of America has a wonderful publication full of technical information, and the organization is far less stuffy than you'd imagine. These are satisfying cars to own and drive, and make sure you get a correct car, it will maximize your resale opportunities.