Why is my Xbox One Controller not syncing?

So I recently put my Xbox One for sale because I am planning on buying the Xbox One S. Instead of using my console to play games and risk breaking it before I sell it I am using my PC to play games with my Xbox controller. Now last week I had my controller next to my monitor and next to that was my bowl of cereal. I went to go use the bathroom and when I connected my controller to my PC via USB and crushed some Far Cry Primal. After about 30 minutes my controller started to get sticky, I looked around the analog sticks to find milk all along with the sticks and some of the buttons. As it turns out one of my siblings hit my bowl of cereal and some of the milk went on my controller. I didn't really think much of it other than it making my buttons sticky so I used a Q-tip, some alcohol and cleaned it, I thought it was fine. Later that night I decided to see what was up with my Xbox and all that jazz. Every time I connect my controller to my PC I have to sync it back to my Xbox, so that what I did. Expect this time it wouldn't sync, I tried for hours, did the troubleshoot, watching videos, it just was not syncing. Soon after that my controller started to "malfunction". I don't quite know how to explain it but whenever I held onto the Xbox controller button it did not flash white slowly, instead, it would only flash or turn white when my actual finger was on the button. Once in a while, it would do the regular "waiting for you to press the sync button" flash. When that would happen I of course pressed the sync button, the button itself would not even make the light flash rapidly unless I pressed the sync button a second time. Even then it still would not sync to the console. I finally gave up and decided to void my warranty and open the controller when I did I found that some of the milk got on the circuits I thought to myself I FOUND THE SOLUTION!!!! So I cleaned it with the rubbing alcohol and made the circuits look all nice and shiny. I put the controller back together and it still wasn't syncing. The controller works fine if you plug it into the console via USB I even tried updating the firmware, but it still does not work. The thing is I’m selling it so I don't know if someone would like to buy a "not anymore wireless Xbox one controller." I’m hoping the smart people here can help me fix it, asap would be greatly appreciated too!!