for the loose shifter, start with shifter bushings... My car did the same thing and it was shifter bushings...
The rocking shifter as I call it will move when accellerating or braking, sometimes only during braking can it be noticed...
As far as the mounts, I say do the shifter bushings, then look into mounts. I think I have read that the mounts are liquid filled but I am not sure if that is correct or not.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.