iPhone 3GS camera lens replacement?

Hi!

I bought a second hand iPhone 3GS not long ago and it's pretty much brand new apart from one minor thing - upon testing the camera, it was completely blurry. I took a close look at the back of the phone to find an annoying dent in the camera, so I am going to assume this is the reason behind it? I've tried using the autofocus and it doesn't help, although it looks as though it's trying to improve things slightly, so I really don't think it's the actual camera. The camera itself seems to be working fine, it takes the picture fine, it's just extremely blurry!

Is there anyway I could replace the lens without having to buy a whole new back housing? I was surfing through ebay and I found the camera lens on its own, but I really don't know how easy it is to replace it this way (without back housing). Thank you so much if you take the time to help me with my question. :)