Perhaps you missed my earlier rant on the 335XI and the CDV:
http://www.e90post.com/forums/showthread.php?t=154713
The short summary re 335XI and the CDV is that it's a little bit more of a PITA than on a 335i because there is a driveshaft in the way when you go to bleed the air out of the hydraulic system. Prob a 30-40min job if you've done one before, a bit longer if you're not mechanically talented and haven't done one.
FWIW I personally wouldn't buy a modified CDV- you can simply just remove it for free, put it on a shelf and just clip the two lines back together again. You're not going to fool the dealer techs because the car will clearly drive totally different and there will be enough marks on the POS plastic bleeder screw on the slave cylinder to tell them you worked on it if they care to check.
It's well worth doing however- you can't even begin to compare how much better the car will drive (ie like a "normal" manual trans car).
