Yesterday, on a whim I soaked that switch(completely submerged) in isopropyl alcohol for several hours occasionally pushing the button down a few times while soaking. I let it dry overnight and this morning it's firing like new. Worth a try.
You said that you soaked it in alcohol and it worked. The switch contacts are sealed, most likely, you're dissolving the gunk around the button that's preventing the switch to full depress and not cleaning the internal switch contacts. That's why I recommended the mineral oil for full switch travel.