Easy. The 230 has the chrome lever for internal lock/unlock whereas the later version has the black plastic lever. The two are not interchangeable because the doors are different.
Mine had been made to
look identical, from the outside, as the later style, even though the driver's door was the old style. I always knew something was wrong and the biggest clue was that the
locking was different! On one door it was locked when the lock tab was OUT and on the other door when the lock tab was IN.
[For those so inclined as to how this is achieved, on the earlier doors I believe, there is a very long rod used for the locking mechanism. Long rods subject to bending, so I guess they changed it to two smaller rods with a pivot point.]
After going to many events from 2000-2017, nobody told me what the problem was. Finally at the Charlottesville event in 2017, Gernold Nisius of SL Tech (who had seen my car several times before!) noted that I had a "230SL door" on the driver's side. When I returned home I started searching for a 280SL door but had no luck in finding one anywhere, but kept looking. Finally one day StevenF from NY calls me and had a line on one nearby from Craigslist, bundled with a bunch of 190SL stuff. His "NY persuasion techniques"
allowed him to free the part from the lot, and we bought it. StevenF was exceedingly helpful in the procurement and shipping. The door sat at Motorwerks in Commerce Michigan for a while, and from 2019-2021 they restored my hard top, swapped the door, and refinished. I offered old 230SL door here in the For Sale section for months with not even an inquiry. It went on eBay and was sold in days to a guy in Las Vegas...