Help me fix my MacBook? This is a real doozy.

Hello! I am hoping some people here might have some advice on what to do in my long struggle to fix my black Macbook.

I have not been using this machine actively since 2010. In January 2010, I accidentally spilled coffee on the machine. I was able to dry it out recover it etc and restore it to functioning, but problems began, particularly with power. It would occasionally not boot. When it did boot, everything was normal, but it basically grew worse and worse as the year went on, to the point that I basically would not use it as a laptop anymore and would just leave it at home in its particular position to ensure I could use it there. Eventually I stopped all this nonsense and got a new computer but that's a separate story.

About a year later I started trying to experiment with using the machine here and there. I found that it would occasionally boot on, but very rarely. More often than not the screen would flicker (including the iSight light whcih would flash green) but it would not actually turn over and start up the machine. If I held down the power button continually it would occasionally just keep going and going flickering. At this point in time I consulted some folks at the Apple Store who basically said there was nothing to do, the logic board was probably shot and it would be very expensive to replace.

Every now and again I would try using the machine. One day I surmised (from reading similar forum posts here) that a new battery might help. So I got one and it did - for a minute. Maybe once or twice though, it miraculously did power on. and if i left it on, it kept going. But if I slept it, took out the power, etc, who knows if it would come back on.

Then it reached a point where if I tried to use it it would be completely unresponsive. No clicks, no flickers, nothing. Finally I took it to an authorized repair place (I'm based in CT) and they did a diagnostic, told me I had a completely shot logic board and the only thing to do was to replace the board. Which still seemed strange based on my experience but at that point it had not turned on for so long that I figured it was probably done.

That was about 5 months ago. Flash forward to today - I pulled it out of a closet and plugged it in, just to give it a try - and bam! the charger worked, the light came right on, and it actually seemed to come directly out of sleep back to the last desktop I had open on it. Completely and totally bizarre. (I backed up some files that had been lost on a subsequent machine right away, of course).

So now I'm puzzled. What do you think? Is this a complete logic board fail? Something on the board that needs repair? A power supply issue?

If I could restore this machine to be functional and consistent it would be wonderfully helpful and also restore my faith in computing forever!

Many thanks for any advice!