For starters SleekTutorials looks very much alike this site that i found on goole whilst looking for my site that happens to have the same name :
http://www.tutorialzone.org/
Now my appologies if this is a script that you can download and install, but if not then its identical.
However if it is a downloadable script and you have heavily customised it then i am sorry for this, just thought i would point this out to any potential buyers.