"I burn everything at 1x!" :doh:
Here's your problem, 99% sure.
Despite what you read here and there on the Internet, you have no need whatsoever to burn at such slow a speed, unless your discs are only 1X-2X specified. Burn your disks at their rated speed, or slightly slower if you encounter any problems with the rated speed.
Many disks give actually worse results at very low speeds. This can easily be checked with quality tests, you can perform them with DVDInfopro on the 109.
Furthermore, the 109 is a high-speed drive and is probably not tweaked to burn at very low speeds. It certainly uses a different laser beam than older models like the 105, so to be able to write at high speeds. Using it to burn @1x is certainly not a good idea. You can never get the best of both worlds in a single piece of hardware...
Try burning at higher speeds (unless, like I said, your discs are 1X-2X discs, then keep on writing them with the 105...). What are exactly your TDK disks by the way? (rated speed, mediacode..)