MacBook Air keyboard & work for login, but not after logged in.

A very small spill of water onto the trackpad / keyboard triggered a failure of my trackpad & keyboard. Strangely though, for the login window both keyboard and trackpad work, but not after successfully logging in. An external keyboard works. I've tried the following:

1) SMC reset via keyboard

2) 'Extended' SMC reset via keyboard by pulling out power adaptor as amber light changes to green

3) PRAM/NVRAM reset

4) Disconnecting internal battery and pressing power key for 5 seconds before reconnecting battery

No joy. Does anyone have any ideas. Much appreciated.

NB Not sure what year the MacBook Air is, prob c. 2013 (I can check later)