I spilled a small amount of coffee on the left shift key of my keyboard. The keyboard otherwise was fine except that the shift key was always ON. I looked up online and there was no solution for fixing the key. Compressed air, key removal and cleaning, nothing worked.
I settled for the cheaper solution of buying a Bluetooth keyboard of Apple. It was great but then I had to buy rechargeable batteries and I would often forget my keyboard at home, not to mention that I had to live with adjusting to typing on this keyboard (which wasn't as bad though because it was Apple's keyboard). Eventually I decided to fix it.
My fix was to buy a new keyboard. I did that from eBay. I don't think the keyboard I got was original but I still gave it a try. It worked.
My fix went well when I followed the upper case replacement guide. A couple of times though, I blocked some cables under the keyboard and I had put in all the screws! My keyboard repair was all complete until I came to the point where I had screwed everything back in place, only to realize my trackpad cable was blocked. I had to disassemble everything, expose the keyboard and unscrew the keyboard partially and take out the trackpad cable.
I used iFixit's 54 tool box and it was sufficient for the most part. I also used that as a tray after removing all sockets to expose the tray.
It will really help with frustration to be organized. Have someone there to cheer you up and boost you: if you mess up it is important to have someone to help you, and say they believe in you. My roommate did that for me.
I was initially reluctant, because iFixIt doesn't have keyboard replacement repair guides. The closest was the upper case replacement. So if you follow that guide, remember that you don't need to remove the hard drive and battery though it will help if you do. You also don't need to go through the guide where it says you should remove hinges for the display and all. A simple guess is to only remove and follow guide until your keyboard is visible completely ...
I also didn't follow the guide in a completely sequential manner, but remember I am someone who has opened his laptop before to replace its optical drive with solid state drive and replace its Bluetooth with newer Bluetooth to make it compatible with OS X Yosemite's features and I have also upgraded to 16 GB RAM.
An important advice is about the display cable, the keyboard cable and the backlight cable: just be careful with them, they go in parallel to the motherboard, and they may not go in all the way so don't push them. Just do your best. But you may break them if you try to push them inside the socket.
Also it's not that bad or difficult of a repair. I know I said my roommate cheered me on, but he only did it after I messed up!
Lastly, I booked an appointment with the Apple Store to check if my repair went well. They checked and approved. It helps and adds extra confidence in you. Yes they will check that for you even though you will tell them you did it yourself. They told me it would otherwise cost me 180 to 240 dollars! That will make you feel good about yourself.