Not working properly and not clicking image

About 1.5 months ago, a very small amount of sea water accidentally splashed onto the camera. It stopped responding immediately. I removed the battery, lens, and memory card and kept it to dry. After 2 days, it turned on, but several functions are now not working properly.

Issues:

1. In Manual (M) mode:

Buttons don’t respond properly.

Viewfinder display switch doesn’t work.

Autofocus won’t click the shutter.

Most settings are locked or show 'function not selectable.'

2. In other modes:

Works partially, but still sometimes buttons don’t respond.

Viewfinder toggle works.

> I think it may be due to internal corrosion. Please check:

Shutter button function

AF sensor and button circuit

Mode dial and internal PCB contacts

> If cleaning or part replacement is possible and cost-effective, I want to repair it. If the motherboard or main circuit is badly corroded, I need advice whether it’s worth it.”