Do you think Rex may be suffering from
Sparkattic arest ?
Well here is an idea :
next time Rex does start , have a volt meter hooked up to him , If the Voltage regulator is letting too high a voltage into the system the black box controlling the spark will overheat and Rex will go into "Sparkattic" arest.
Maby we should start a new topic "What could it be , The REX delimma"