I have the same cap on my early '63 230SL. I bought a chrome cap and when locked I can pull it off, not good. The early cap is better made and very secure.
I believe it may be for a W111. It is built like a tank.
Mine needs a replacement seal and has no key.
I do not see any key code on it.
The only 2 reasons at this point to disassemble would be to see if key code resides inside some where or to see if tumbler could be replaced for one with key.