Read this recent thread:
w124 tranny...3/4 - 1 inch of play in the shifter between 3rd and 4th gear, normaL?
and do a search on "shifter bushings". Parts are cheap, and the process takes more or less an hour.
The confines are narrow, which is the only challenge to the repair...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car