My trackball is a complete pain in the arse. If you have the time, it would be worthwhile to take the battery out and keep your phone in a jar of rice overnight. The recommended time is 3-5 days but i couldnt live without my phone for that long. If the problem was with the other keys then i would suggest re-installing the operating system but it seems to me that moisture is the problem. Your last resort is to just buy a replacement keyboard in the internet, they arent too expensive. Theres no point in giving your phone to someone to get it fixed for £50 when you could do it yourself.