Some of my BlackBerry keys won't work?

When I type on my BlackBerry Curve 8520, it used to type the letters normally. Now, when I type the letters 'B, N and M' nothing appears or changes. I split a bit of liquid yogurt (YOP) on it, I think that it seeped through to the keys but it was fine until the next day. I then got a little drizzle of water on it the next day but it OK for about an hour. I went to text my friend and the enter button kept sending the messages when I typed something wrong and pressed the backspace button, I really need help on how to fix this. I checked every where online and nothing has fixed it! I think I should take it back to O2 and send it away to their warehouse but will this cost much? I just need a second opinion! Lots of points to the best, quickest answer!