[Richard]

I hope I am wrong too

I spent a long time looking at Tuga's. It was rusted right around the area where the exhaust pipe exited the boiler. It was definitely rusted form the inside. This would be in contact with the coolant. My thinking was that the rust inhibitor in the coolant was long gone. After all how many would change the coolant in the AH. I added a pint of rust inhibitor to mine soon after. I don't know of a way to check the inhibitor content without access to a chem lab. The ethylene glycol which is the primary ingredient in coolant does not go bad with time. You change it out because the inhibitors and anticavitants are consumed over time.