Hello, new here. I sent an e-mail to mbdoc a short while ago, but have decided to post the question on the open forum to possibly get more correspondence.

I have an 06 c350 Sport w/ 6 Spd manual. I have the 2.83 gears as
stock. I'm trying to do some modifications to make it a little more
fun to drive.

Ive been trying to hunt down an OEM w203 pumpkin salvaged/used w/
either the 3.46 or 3.67 ratio. Apparently the 3.67 was available with
some of the c240s (2002 seems to be the most popular year for this),
and Ive found a 3.46 from an 05 c230k.

It seems that buying the whole diff and swapping it will be a cheaper endeavour than rebuilding my current pumpkin with new gears. So...

1) Will any w203 rear diff be a direct physical swap into my car? If
not, what parituclar diffs will interchange? If you're not sure, what
do I need to look at on my rear diff to match up with the donor diff?

2) Which w203 would have came with 3.67, 3.46? (if they'll swap over)

3) Im having my ECU flashed by a tuner. They claim to not have the
capability to accomodate the new gear ratio via their flash. They are
telling me it needs to be done by SDS in developer mode, and that any
mbtech should have no trouble with this (I'm not so sure than just any
mbtech would know how to do this). Supposedly otherwise my speedo and
ESP will be awry, and will possibly go into limp mode. Do you know
what needs to be done with the ECU to make this happen? Since I have
the 6spd manual, I have no TCU to deal with to fix this.

Thank you all for any help!

Cale