It is always fsacinating to see this type of article as it gives an insight into how the equipment works and what the manufacturers are doing. Build quality is mainly fine, although it lacks the modular constuction of the latest Canon lenses and screws really should not work themselves loose. Rather than have a continuous production line, companies often build lenses* in batches and only make more once stocks start to run low. It is not unknown for a more exotic lens to be discontinued at this point** and replaced with a new design. Although Tamron could easily fix the problem in the factory, that will not necessarily happen. The other thing to point out is that this lens has a fixed hood and replacing it requires complete disassembly. That sounds expensive, so my advice would be not to break it in the first place.
http://www.lensrentals.com/blog/2015/06 ... l-teardown
* Maybe certain cameras also? I have heard suggestions that Fuji only made two batches of the X-Pro1. One for launch and the other in 2014.
** Does that explain the long time that the original Canon 100-400 remained current, I wonder?