The bold part above is most interesting. This would seem to support the dissimilar metal corrosion theory and would indicate this occurs from the inside out vs external corrosion working its way inward.This happened to ours last year with 170,000 on it. Luckily my wife is one smart chik and shut it down immediately.
Getting it towed home (I always seem to be at the firehouse when these things happen) promptly and we were able to repair with no lasting issues to engine or transmission.
As I do as much work as possibleon my vehicles, I am always looking for wear and maintenance issues and there was never noticeable corrosion or advance warning for it.
We are getting ready to turn over 200,000 on it though and that is the only major problem we have had and I do a lot of towing with it.
So still happy with the Ridgeline.
I still maintain the safest course of action is to replace the radiator when you do the TB/WP service.