corrosion between motor and engine housings caused by coolant leak?

[yogaguy]

I had a pressure cooland leak test done, which didn't come up with any internal or external coolant leaks, but was told the test wasn't definitive. I smell coolant pretty strongly in the engine compartment, and I saw strong signs of corrosion between the motor and engine housings (location described by a friend, so I'm not sure how accurate his description is--but I definitely saw the corrosion).

Anybody know about this, how serious it may be, and any helpful solutions?

thanks!