[Booger Welder]

There is some missing information here - such as what type of radiator you are talking about.

There is a simple 2 core radiator and there is Double Pass radiator. The double pass ones - you shouldn't crimp off the flue.

You also have to understand that the flues are furnace brazed, where they put the radiator inside a furnace and they heat it until the flues melts to the tank. When you start heating that stuff up - you run into a whole mess of problems.

Places like C&R racing radiators has a shop where you can send a radiator to be repaired professionally. It usually requires the flue to be removed and replaced.

The only other thing you could do would be to cut the flue at the tank, Cut the flue about a inch away from the tank. Weld each piece solid and pressure test it to make sure that it does not leak.