Getting Slower

Hello I am learning Flash and Action Script. I just made my first game as self practice by using Flash CS3 and Action Script 3.0. It works ok but the longer I play, the slower it gets. I used timer to let the images to be loaded couple times before they stopped, so it will look a bit more like real machine (although the real machines are “rolling” the images) Here is the link for the game:

I searched online and found people talked about “memory leak”. Is my case relate to “memory leak” problem? But my game is a very simple game. How can I solve this problem? Here is the flash file:

Also, I am still learning Action Script 3.0. If anything in my code should be improved, please let me know.

Really Appreciate…