I wonder if its standard for gdrom's to have bad sectors.
I tried to burn the 99min Disk 1 CDI with Alcohol 120% and ImageBurn, have wasted 3x 100min disks already
and the Nero CD/DVD Speed tool always shows me defect sectors with the surface scan on the same place on all three disks :/

edit:ok..that seems to be normal...I have that red stripe of defect sectors on every disk cd1,2,3...its of equal size everytime ^^

edit 2: Successful Burning

Brand: Best-CDR 100min
http://www.ebay.es/itm/282067099116?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Media ID: I 12:46:54 Destination Media Type: CD-R (Disc ID: 97m27s58f, Mitsui Chemicals Inc.)

Dreamcast Model: PAL VA1

Shenmue Undub Disc 1,2,3 boot instantly.
But I had to test 3-4 cd-burners I had at home until i found one that worked in terms of producing easily readable disks for the dc.

I didn't tests the disk with longer gaming times or so, so I can't really tell how reliable this disks are in the dc.

I burned with a Samsung SH-S223F, 16x, ImgBurn