Scholtés Gas Hib, Electric ignition

Dear colleagues,
We have a Scholtés Gas hob in our kitchen, installed 1981. Model number is T 478 Gee Lux Inox UK 3180466. It has a mains electric ignition system, controlled by a push-button on the right front corner of the hob. For about 10 years this has not functioned. I have investigated under the steelwork and tried to see what can have gone wrong, and after one attempt to clean it up it did work for a few weeks before failing again.
I should be very grateful if someone can suggest where the fault lies, and how to tackle it.
TIA,    Robin.
Robin Phillips,
Beeston, Notts., NG9 1BT
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