Kemal,
My 1968, 280 came with three keys. One for the ignition, one for the doors, and one for the trunk. Either door or trunk key will open the glove box. Add a locking gas cap and you get another.
Dermot,
You didn't say what year yours is. I presume you tried the key in the other locks. Do you have access to a parts diagram? It helps to look at that before you disassemble it. It isn't too conplicated even if you don't. Just pay attention to how it's put together before you take it apart.
Ray
'68 280SL 4-spd Coupe