Some keys on the keyboard fail 80% of the time
I have a mid-2012 13-inch Macbook Air, with OSX Yosemite installed.
The keys on the third column on the keyboard, [F2], [2], [W] and [S] fail to work very often. It's not always, sometimes they do work ok, then stop working randomly. They also do not fail when using Windows in a VM.
The fact that they do work sometimes suggests that it's not a hardware issue. But they really fail a lot, which as you can imagine drives me crazy. Everytime I have to type something, I have to run the Keyboard viewer and press every [s] and [w] manually, or use an external keyboard.
I've tried resetting the NVRAM, wiping the hard disk and starting a new (not restoring from backup), but nothing works.
I'm out of my wits really. Please help.
MacBook Air, OS X Yosemite (10.10.3)