If ignition box is the problem, you have nothing to lose by taking a look inside. Admittedly, that cold prove difficult because it might be sealed with an epoxy resin. However, if you can dig the epoxy out or cut the unit open, you might be able to see the component parts. If the unit is a capacitor-discharge type, a lot of the times it is just the capacitor that's gone faulty, in which case you could try replacing the capacitor for a few quid. If the unit's knackered, there's nothing to lose except a bit of time.