Before you try this, make certain NOTHING else has worked to solve the problem. NOTHING. And that you are ready to replace the keyboard.
This was used to fix a laptop that had a coke (yep, real coca-cola) spilled on it, and it worked, but it had to be taken apart and cleaned part by part.
Buy some DISTILLED water. Be sure it is distilled; everything else (tap water, spring water, bottled water) has minerals in it and can leave residue after it dries.
Also buy some 91% or 99% isopropyl alchohol. You will need several bottles. (I have found 99% regularly at Safeway stores, and most Walgreen type drug stores will have 91%)
Wash the keyboard in the sink filled with the distilled water. NO soap. Move the keys to help the water clean the gunk off.
Drain the board as best you can.
Now, soak the board as best you can with the alchohol; if you bought enough to put in the sink, then soak it. Otherwise pour it all over and into the board. You want the alcohol to absorb as much of the water as possible so that it will dry better and faster.
Let the board drain, then hang it in a warm place (it's summer here in the west, I would put it in the garage where it gets really hot) to dry but not in direct sunlight; you want it hanging to avoid pooling of any liquid. LET IT DRY FOR 4-6 DAYS! LONGER IF YOU WANT! IT MUST BE PERFECTLY DRY INSIDE BEFORE YOU PLUG IT IN. Feel free to use canned air, or an air compressor with the pressure at 40-45lbs (no more) to blow out as much liquid as you can when you first hang it. Might also want to change its position/rotated it the first couple days.
This is not a completely original idea: True, my friend saved his son's laptop about 10 years ago doing this. And the alcohol treatment was my idea at the time. But I believe Maximum PC magazine published an article several years ago outlining this drastic keyboard cleaning method.
Good Luck. And remember, you should be at the end of your rope with trying to fix it before you try this cause it can kill the keyboard.
P.S. You will be able lay serious claim to your monicker if this works Mr. Nick_Haywire!!