The fuses are encased behind a plastic window perfect for condensation to form inside this is the reason why the corrosion forms but it does protect and keep it dry.
You have to open the window to access and so the terminal is best if you removed.
Corrosion in these areas are a worst nightmare for electronics.
Something I really dislike to see but the wd40 can work and I have seen this to be used on circuit boards so is as safe as the contact cleaner.
