I'ts probably an early failure of a seal, and the kit has a better seal in it.
Any good tranny shop that deals with MB can do this, it's not a terribly difficult job, but the mechanic MUST be familiar with the transmission!
Filter and fluid change isn't a bad idea, either, as a plugged filter can also cause shifting problems.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!