Have you checked the car key itself?
The car has a valet key I believe that will not opent he trunk or locki the glove box when locked with the master key.
If you can see that a piece is actually not attached, then most likely you are in need of the lock view.
If I had the manual for the w201 chassis, I'd post it up for you.
Hopefully, someone will answer this for you soon. Give it a little time, sometimes you wont get a response right away.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.