I wouldn't go cutting on the transmission lines.......Mercedes made that line metal for a reason.
Can you provide some additional details on when the transmission is shifting hard? Is it when the car is cold, does it shift hard in all gears or just 2nd to 3rd? Hard acceleration?
Does it get better or worse ever or is it common problem?
Could be a weak pump on either end of transmission......
Fluid could be low.....or old.....
Any evidence of leak and/or road damage?