Fuze 8GB Issues - How to Warranty

I have had this about six months and I started only getting one channel in my headphones. I changed the headphones and the problem still exists. So if I play with the part that plugs into the jack I can get both channels but when I let go it goes away. I notice that the plastic ring that goes into the Sansa is also cracked a little. 

So how do I get a warranty replacement for this?