Spilled Water on Macbook Pro keyboard, can I repair this?

I have a 15" mid-2012 unibody Macbook Pro, A1286. About two weeks ago I finally upgraded the internal drive to a 1TB SSD and it was like a dream. Then this past Wednesday, a caught peripheral cable knocked over a nearby glass of water onto my keyboard. I immediately flipped it upside down and mashed the power button, got impatient with the auto-shutdown and selected shutdown with the keys (while still upside down). I let it sit, open and main case upside down for 96 hours.

Monday morning I follow a take-apart guide to make sure I don't see any water inside. Once I realize the keyboard area is pretty much sealed off from the rest of the machine I put it back together. I press the power button and nothing. I press and hold longer and nothing. I check the battery level indicator is full. I plug the power cable up to it and it starts booting like normal – without me pressing the power button again. I give it some light testing, all keys work with the exception of left side Shift, Control, and Option. I shut it down to start researching that issue.

Later in the day I try booting it again on battery and nothing. I follow the same procedure as before and it boots after I connect the power cable. I shut it down again, wait a few moments and try booting again and nothing.

So basically the power button doesn't seem to be fully functional at the moment. When I did get it booted up I didn't try powering it down by pressing the power button, just through the menu. Seeing as I have some dead keys as it is, would this be worth trying to fix on my own? Does this sound mostly like swapping out the Top Case (Upper Case) would do the trick? There's a huge discrepancy between new and used prices for Top Cases – $300+ new, $20-40 used based on cosmetic condition, which I don't care about, so if this could end up being a $20 fix I'd be sooooo happy.