Does the car have miles on it with the braze in place? If so look for cracks in the brazed joints. you may want to use die penetrent to detect the cracks if there is any. The reason I mention this is that if there is cracks that means that it is over stressed and you will have to replace it with steel welds. The rear of the car counteracts twisting of the structure so look at areas near the corners of the braze joints. You may need to sand down the brazed joint to make it smooth in order for the die penetrent to work.