When I worked in garages as a kid, the first thing I did getting into a customer's car was stomp on the brakes. I had several fail right away because of that.
Also, I know personally at least two people that had complete failure with the dual system in a Chevette. I think it was probably in the design of that horrible little car!
One thing I haven't seen mentioned is the installation of a brake warning light for the dual system. I know that it is a complication because of the valves and extra plumbing involved. I think in a custom setup it might be possible to adjust things in such a way that only one system was working.
