Hi, Jean-Paul,
If your antenna is original and fitted at the right place (320mm [12.6 inches] from the edge of the wing [fender] at the door gap), it will be accessible from the 'inside' of the car. The kick panel is the soft sided panel that you have removed from the right side where the passengers right foot would be.
On my '65 car, there is a big cut out in the inner panel, so you can get your hand around it. Once you undo the nut on the wing (fender?), you can drop the antenna into the cavity and take it out. There may be a small bracket holding the bottom of the antenna tube to the inner panel (often not fitted on light manual antennas).
Maybe someone with an earlier 230 can advise if the cut-out in the panel is there?.
The same panel on the left of the car is solid and I cut a round hole in it to fit a speaker.
If your antenna if fitted further forward, then it could be accessible by removing the splash guard (bolted door) from the wheel arch.
Not much help hey???
naj
65 230SL
68 280SL