Corrupt keyboard problem

I have MBP 13” mid 2012. It is very clean, doesn’t get used much. Today I became aware of keyboard problems. I can’t get out of CAPS when typing with the native keyboard. It also boots into ‘safe boot’ all the time. I have plugged in a USB keyboard which doesn’t share the problems. Here is a strange one – I tied to boot into another version of OSX, a have a few on an external HDD. When I hold the option key down during boot up it goes straight to the OS without stopping for the password. The only way I could boot into an external OS was to use the ‘startup disk’ setting in system preferences.

From what I have found on-line so far it seems to be a problem with the caps lock, shift key and maybe in this case, the option key. It is mostly caused by spilt drinks getting into the keyboard. Not only has this not happened by I also have a silicon keyboard protector on at all times. The keys all move freely, the shift key functions correctly as does the option key. I just can’t get out of caps and it boots into ‘safe boot’.

What can be wrong here?

 

Ok I have worked out that it is a stuck Shift key. and the solution could be what is posted at the end of this thread https://discussions.apple.com/message/21690381#21690381

At the moment I have removed the key cap and the plastic scissor bits and have the keyboard viewer up. The shift key is lighting up and dying all by itself but can also come on and off randomly if I push the nipple. Something is amiss under that key and it looks squeaky clean. I thought Macbooks were better built than this.