My MacBook types 2 letters when I strike the "U" key

My MacBook A1181 Core 2 Duo Early 2009 (serial YD9240NA4R1) suddenly began to type "ru" whenever I strike the single "u" key.

I first noticed when it would actually type the same when I would strike the "r" key but now it only does it when I strike the "u" key. I have the problem in all applications and can actually see the double key strike in the virtual keyboard viewer when I type on the physical keyboard with the keyboard viewer pulled up. if I type with the virtual keyboard, there is no double strike.

I have already tried resetting both SMC and PRAM and adjusting the keyboard preferences to no avail. I have lifted the keys to ensure they are clean and that the scissors are functioning properly which they are and I have lifted the entire keyboard to ensure the cable is in good repair and the connection to the logic board is secure. All looks good.

I have recently made a few unrelated repairs but finished with the last of them about 2 weeks prior to this sudden problem. The computer was exposed to a small amount of water about 6 months ago. After drying out it worked just fine. About 2 months ago, the LCD backlight began going out. I replaced the inverter card and cable during trouble shooting then about 2 weeks ago replaced the entire LCD panel which fixed the problem. During this time I also installed a new Seagate 750gb hard drive and upgraded to Mac OS 10.8.2 from 10.5.8. The machine had been working just fine for 2 weeks since I completed these repairs/upgrades until I suddenly encountered this new problem.

Any ideas other than replacing the entire keyboard?