[rotorwrench]

Steel is good for a lot of things but it isn't a very good conductor for high tension electricity. My guess would be a crack or corrosion. A person would have to break the plastic apart and look at it. Copper, aluminum, and brass are the normal metals used in the construction of distributor caps and the like. The old model A distributor body or cap assembly had likely been made out of all sorts of materials over the years. Steel was likely used to hold the spark plug terminal conductor strips better. The design works but I like the B distributor better.