I just did this on my Z4 Coupe and presume that the process is similar. With blue masking tape, mark the position of each wiper blade (leaves no marks if it is sunny out). The plastic cap pulls right off the windshield wiper hub nuts. Raise the hood. I believe that I used a 15mm wrench to loosen the nuts. With a little wiggling, the wipers come off pretty easily. I found that my cowl was held in place by 4 plastic "buttons" along the front vertical face on the firewall as well as about 10 pins that press in to mounting holes in the horizontal surface between the firewall and the base of the windshield. The 4 buttons can be carefully pried out with a putty knife. You may need to unscrew the center pin to these buttons (some are looser than others). Replacements can be purchased at either the dealer or a local auto parts shop (I got mine at Pep Boys for a buck). When these are out, you can pull the old cowl piece up from the edges. You will now see how it was held in place. Remove the white inserts from the mounting holes if they are obstructed with the old pins. They come right out with a pair of needle-nosed pliers. Wile you have the old cowl off, vacuum out all the accumulated leaves, etc. from the drain holes. If you are as obsessive as I am, you will clean and wax this hidden area to protect it while it is accessible.
The new cowl will come with white inserts mounted on the horizontal mounting pins. I removed these and inserted them in the mounting holes as needed. I also found that I needed to remove a little flashing from the edges of the new cowl with a razor blade before mounting it. The new cowl presses into place easily. Secure the front edge with the new buttons, remount the wiper blades and nut covers and you are done. The whole thing shouldn't take much more than 30 minutes.
Last edited by papak; 10-07-2012 at 06:29 PM.