1. Walk around the 230 and look for any impact dents. If the sedan was in a crash then the dents will be knee high and could indicate structural damage in that section as well. Go below the car and look at the car frame for any deformations of weld lines. The frame will have weld lines where the struts meet, but if there is a weld line in the middle of a strut then that means it was snapped in half and re-welded. Do not buy a re-welded vehicle, as this compromises the car's ability to survive a crash.
2. Look for any rust on the frame and body. Rust will show as a brown patina that indicates oxidation has set in on the steel. Rusted body panels can be replaced, but rusted car frames cannot. Pay special attention to rust on the metal straps that hold up the muffler as these are often the first ones to go.
3. Look at the disc brakes for any signs of warping or worn-out brake pads. The 230 was notable for including vacuum-assisted disc brakes as standard in an age where drum brakes were still prevalent. However, hard use or accidents could warp the discs and make them less efficient. The brake pads should still have pads in them, though it is likely that the original Mercedes brake pads have been replaced with third-party ones due to the exorbitant cost of vintage Mercedes parts.
4. Press down on each corner to test out the spring suspension. The corner should bounce back up immediately. If the corner takes a few seconds or if it stays down, then the springs are shot and need to be replaced. Springs wear out over time, especially in heavier cars like the 230. Visually inspect the springs for any cracks. If the spring is cracking then it is only a matter of time before it snaps and becomes useless.