Cox Dragonfly Tanks are Cracked

I planned to put a Cox Dragonfly 049 on my foam lazy bee. Gave it up, to drive Truck, across USA. Had found Monster Trucks, to run @ Truck stops, but back to Nitro and Diesel now, hehe. Pro @ Davis, told me to run nitro first, then diesel. Dragonfly 049, would not pull fuel. Tried 5 types of Cox reed valves. Blew air into the suction nipple, and could see the air bubbles, coming out of a tiny hairline crack. Then I tried a white Ranger 049 production tank. Engine would run. Even with needle valve closed, or removed. Changed the reed valve to mylar, and installed a new spray bar seal, under the needle valve. Still no success. Are all of these Dragonfly 049 tanks no good? Appreciate any input. Thanks,
dj