Engine will not start

[Angus]

Hi - I have a 1987 240GL Auto Estate, petrol, with the B230K engine.
No spark can be found. The engine runs perfectly for eighty percent of the time, but on parking and switching off engine, it can refuse to re-start.
The exact contactless ignitition system does not seem to be in the Haynes manual. No normal coil exists - appears to be a transformer working from an impulse sensor. Local mechanic has failed to cure fault. Any suggestions would be much appreciated!