(I also put this somewhere else, maybe the DIY forum.-SC) Okay: I am finally a member of the Hydraulic Fluid In The Armpits Club. That is, I finally got around to yanking out the CDV and replacing it with a bored-out version from Zeckhausen. In the Z4 M roadster, it's a ridiculously simple procedure. Click here to read a discussion of the advantages and procedures on other models; you can read Zeckhausen's analysis of the situation here. I noticed the difference within a block of La Jolla Independent, where Carl Nelson kindly allowed me enough lift time to perform this minor surgery. I no longer feel like a fourteen-year-old trying to master his first manual transmission! Best of all, the "ka-chunk" engagement of second gear---which I believe will eat the synchros sooner than later---seems to be significantly diminished. Michael Bird is currently writing up the CDV procedure for Roundel, as he is another passionate advocate of this procedure. I could have written such a story myself, but my hands were all slippery and I couldn't work a camera.
You are so right about getting rid of the CDV. A couple months ago I decided to not only take Mike Miller's advice about fluid changes but to also visit various forums to learn what else could/should be done to my 2006 E-46 M3. One suggestion was getting rid of the CDV (which I, too, replaced with the Zeckenhausen unit). The difference in shifting was phenomenal. No longer, like you, do I feel like I'm learning how to drive. And I'm inclined to think the replacement of my clutch, flywheel and t/o bearing (the only car in 40 years I've had that has needed these replacements which includes a few with over 100K miles) at 65K would not have been necessary had the CDV never existed.
