Hi,
So I'm continuing this project and Brian from AD advised I should plumb the hot water heater return to the front of the heat exchanger (not into the expansion tank) and I see our friend Chuck did this as well:
The Trawler Beach House: Mystical Water Heater and Engine Hoses
But once I got the expansion tank off I found that the large outlet on the starboard side was repaired at some point in the past with JB weld and has begun to fail. So I'd like to replace the tank or get it welded properly. I see on eBay a new steel tank is priced as though it were made of Gold. So does anybody know what material the original tank is and can I weld it?