I get these at Home Depot and Lowes, they are only about half that price in the store though.

http://www.homedepot.com/Outdoors-Grill ... reId=10051

In my experience working with many brands of these, I am an Industrial Automation Maintenance Technician, the most common reason for leakage is due to the male disconnect, but not being damaged where it mates to the seal, but at the flared area where the balls inside the female fitting rest on the m...

You could use threaded inserts in your casting, that way the threads aren't directly in the bondo and the force from the repeated screwing(lol) would be distributed to the casting more. Just a thought.