Maybe this will help:

The "B" pillar trim is held on by an extremely strong double-sided tape. Just pull it off from the top (I used a chisel, wrapped in cloth, and inserted it at the top, where the missing plastic piece should go). You will destroy the old trim piece in the process.

The hard part is getting rid of the tape residue - it is REALLY tough stuff, and all of it must be removed or the new piece will not fit properly. I used all kinds of stuff - mainly "Goop-Off" (Goof - Off?) adhesive and glue remover, and fingernail polish remover (acetone).

Just be careful when installing the new piece. It inserts between the door and the window trim at the bottom, and you'll only have one chance to get it right. Position it and get it into place (for practice) before removing the paper that covers the tape on the new piece.
__________________
Warren

2010 S550 w/AMG
Sport appearance package

Formerly:
2005 S500 4-Matic
1978 450SL restoration project
2000 S500

I also read somewhere that if you carefully use a heat gun to release the adhesive you may be able to reinstall the same piece of b-pillar trim. I know you said yours is damaged, but I thought the heat gun idea would make removal easier.