But one question from reading this, what's 'Electrophoresis'?
Electrophoresis was the application of a zinc phosphate paint undercoat using an electrically charged dipping bath, it was developed by ICI in Australia, but it was already a common process in European car manufacturing. In theory, dipping the body into the electrically charged paint bath (the bath was negative, the body positive) caused an even zinc phosphate paint undercoat that covered all normally inaccessible areas such as the interior of box sections. Apparently there was a time where the temperature of the bath was incorrect causing incomplete coating in places. Over time a lot of the cars involved (over the 1970 - 1972 period) rusted out prematurely, usually over a period of 12 - 18 months.
Also a secondary problem, not associated with the Electrophoresis process. Was where a number of cars over the same period suffered from excessive heat application, which caused the undercoat to peel on the interior of the box sections (such as the sills) that also caused premature rusting. The problems were resolved by 1973, and by 1974 there were further rust prevention measures introduced.