It is not a manufacturing defect. The initial failure is caused almost exclusively by impact. Any failures after that come from problems related to the first breakage that are not addressed when you replace the header.
Breaking your header can be caused by a number of different things and sometimes it is a combination of problems. Generally it is due to the pipe impacting or vibrating against the header. Set the pipe 1/4" to 3/8" from the header so that it has the room to flex without hitting the header. Adjust the pipe hangar so that it is lightly pulling the pipe away from the header once it is attached. Replace your exhaust coupler as well. Once it is worn out or damaged internally it cannot prevent contact between the header and the pipe.
Other culprits could be broken/stripped rear body mount or screws, or a broken engine mount. You typically see stripped spur gears with the broken engine mount.
If you are still having problems then adding a wing will protect header. Your best source for this would be your local Traxxas hobby dealer. You can find your nearest U.S. Traxxas dealer at this link!
http://www.traxxas.com/products/trx_products.
It is true that others have had the problem as well. The same solutions apply to them that I gave to you. It is not an issue with wall thickness no matter what they say on the forums or all of the headers would be failing. We have many tens of thousands of these headers out there in regular operation. All the issues you can find on the header will not add up to one percent of the total.
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