It makes it easier that you have the old grill off. Get your self some Vise grip pliers, squeeze the spring clips underneath, and turn 90 degs. It should come out. Part of the base for the hood ornament, there are 2 "keepers". Once you squeeze the springs, you need to turn it as such that the springs tuck in behind these keepers. When you put the ornament into the new grille, just by twisting the mechanism, the clips will pop out and hold against the underside of the grille. I had to do this when I replaced the grille on my wife's '87 TD.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member