Old water damage - slow trackpad/keyboard speed

Afternoon,

I have a macbook air that sustained water damage along time ago - I have no idea what steps were taken by the family member in question, but they probably weren't the correct ones. I would say this was bordering on a year ago or so, and has since been gathering dust in a cupboard.

I've switched it on, performed an SMC reset, PRAM reset, re-install of the original OS.

I have taken the back cover off (and as was probably more than reasonable to assume) there does not seem to be any moisture or water under the chassis or anywhere else.

The laptop works fine - connects to wifi, usb ports work - everything seems fine. EXCEPT everything is just a bit slow, the cursor moves slower than it should with I use the trackpad, and it's the same when I type with it, and of course navigating through progammes and menus is a little slower than it should be

In addition the fan is running very loud

What could this be? Any idea what i can do for a fix?