Like so many things that are so old, it might need some gentle persuasion.
It is entirely likely, too, that you will NOT be able to remove the bulb without destroying it. The glass part of the bulb might separate from the metal base. In that case, a needle-nose pliers will be required to remove the base from the holder, and of course you'll need a new bulb.
Been there and done that as they say.
Michael Salemi
1969 280SL
Signal Red 568G w/Black Leather (Restored)
President, International Stars Section
Mercedes-Benz Club of America