W163 auto box spring broken?

[m11nch]

Hi I've got an 2005 ml270 and when I put it in drive the car drives great
But if I try to use a manual gear the box will "jump it back up to drive/auto"
As if there is a spring keeping the shifter permanaly right
If I carefully hold the shifter and drop a gear it will stay in that gear But I would really like to get my motor to the best I can any ideas on what and how to solve this problem thanks

 

[DrX]

If you're a keen DIYer you could disassemble the shifter to see if there's a broken spring. The easiest way to fix it might be to swap in a used shifter from a breaker's.