Replacing hardisk.
 

Recently the harddisk of my Zen Sleek broke down, and I decided to check it out.

The harddisk is labeled Toshiba MK2006GAL and is available at 25$ on e.g. Amazon. The harddisk is similar to the one used in iPod 4.

To replace the harddisk with a CF card, an adapter is required. Google: CF to 1.8 Toshiba IDE Converter

Haven't tried the CF solution yet, but will return if I stumble over an adapter.