>the dies wear out! This is not a new problem - it is inherent in the manufacturing process.<

Basically, the thickness of an aluminum extrusion can be controled by the temperature the billet is heated up to, and the pressure to ram it through the die(s), resulting in the exit speed of the new shape from the extrusion press.
As a die ages one can vary temperature and pressure to control thickness. Sometimes it ends up being a lot of scrap depending on the allowed tolerances. (we are talking plus/minus thousands of an inch)
A decade ago, it use to be more of an ART than a science to get the temperature and pressure right, maybe that has changed now.