Thanks for all the constructive comments on my first post about the corroding terminals on the back of this unit. I've had a reply from Garmin.
Thank you for contacting Garmin International. The unit is not waterproof, rather it is water resistant. We will honor a warranty repair this time however any future water damage will not be covered under warranty.
Not waterproof? Garmin's own website says: The card slot is located inside the waterproof battery compartment, so you don't have to worry about getting it wet."
And under the unit Specs it says Waterproof: Yes (IPX7) An IPX7 designation means the GPS case can withstand accidental immersion in one meter of water for up to 30 minutes.
Amazon's description from the manufacturer says: This waterproof device also floats in water. You can recover your device very easily if ever it slips overboard.
I've asked to take them up on their offer but also requested clrification. I'll keep you posted.