Why does the left triger button not work?

I’ve had my gameboy for a good amout of years. Never had any problems, but for some reason the left trigger button stopped working. So I bought one of the little three prong screwdrivers to open it and check it out. Cleaned it out, a lot of dust, figured it was that but wasn’t. I closed it back up and still did not work. Both of the springs for the triggers are working fine and I hear the clicking when I use them, but it still does not work. My guess is it’s something to do with the button like I have to get it replaced is my guess. But just wanted to get a second opinion.