How corrosive is coolant?

Gees the wife is a chemist,, thats cool, just don't let Ben Cousins around.. lol

Anti Freeze formulated with Ethylene Glycol is not corrosive in the sense that it will initiate corrosion of metals, as well it contains corrosion inhibitors for iron and non-ferrous metals eg copper, brass, zinc.
What is does do when spilled into crevices is that unless it is completely removed it will oxidise over time and absorb moisture from the atmosphere. The oxidation/decomposition products can promote corrosion between adjoining metal surfaces.
After you gently hose it out spray the cavity and crevices where it has been with Lanotec or similar corrosion inhibitor. That will displace any residual moisture and coat the surface effectively against corrosion.

Thanks Mate, good advice.