When I bought my '85 300D the same thing was happening on my glove box also. If you open the door and look at the corners of it you will see 2 nuts. These nuts hold the whole door/cover assembly to the dash itself. Once you get the door off you will see the whole mechanism. The spring is probably out of position. It looks kinda U-shaped and is metal. This should be vertical and the latch should be between the arms. When you put it between them and then push the latch to one side, you will see how the spring forces the latch to return.

That is the best way I know to explain it. Hope it wasn't too confusing.

Good luck,

__________________
Frank
84 500SEL EURO 101K ( JUST LIKE MY 1ST WIFE. GLAD TO GET RID OF HER! )
85 300D 310K (sold)
90 350SDL 184K sold
83 300D 118K (sold)
88 300E 153k (sold)
93 400E 105K (sold)