Well, I have been trying to chase down a coolant leak. It has taken me over two months. I did find a small leak as I posted on one of my coolant hoses and replaced that one but I was still adding some every 500 miles. So the search continues. If you have an aquahot and it is an older type unit, look in the aquahot for the motoraid side. It has elbows that crack and that allows a small but steady amount to come out. It will stop when you shut down and it will start up when it is running. SO you may not see it unless you crawl inside and pull off the covers.
John, my situation pretty much matches yours. On the Upstate NY Motorcade, Jack Bradshaw found , what sounds like, the same AuquHot leak at a 90 deg elbow on the engine coolant loop. He also found a slight leak on the bottom forward corner of my radiator. I'm using Barrs for now which is keeping it under control.
I think I also have a fuel line allowing air into the line to the AquaHot. I replaced a 12" piece just after the fuel filter which helped for about a year.
Some one, on this site I believe, suggested that after 10 years all rubber needs to be replaced.
At 12 years I'm over due. Not looking forward to the top of the tank issues. I least dislike the idea of cutting through the floor from the solon, as described by some one earlier on this forum, if we can do it nicely without destroying a perfectly good carpet.
You can pull the pump and the burner and take out the offending section and replace it.
As for lines, yes we will have to do that soon too.