The issue with liquid damage on any device is that it causes corrosion that spreads over time. Usually liquid gets under chips on the motherboard (and you can never be 100% sure you get it all sorted because you can't see underneath these components). Chances are that you will see more problems further down the track as this corrosion eats away at the solder joints on the main board. I would assume that the guys you took it to tried a new battery in it, maybe cleaned the board a little with isopropyl alcohol and sent you on your way.
To be honest mate, this could end up being a lost cause. My suggestion is to backup anything on the hard drive that you care about or need if you haven't already "but you seem like a smart fella so i bet you already did that ;)" and run the thing into the ground. Or try contact apple and see if you can sort something out with them.
If you wanted to attempt to fix this then you would need access to an ultrasonic cleaner with a big enough basin to house the motherboard and try treat it with that. Only problem you can have is that since corrosion eats into the solder points. Once it's cleaned out with an ultrasonic cleaner, this leaves a void in the solder joints which may actually cause the device to work worse or not at all, so it's a bit of a gamble really. Sorry to hear about your problem mate and I wish you luck in your endeavor to get it sorted :)