1993 Model with Misfire (again)

[THERACEFACE]

Following my previous post, a local garage discovered a crack in the new rotor arm causing my misfire  and replaced it (not the injector wiring as first thought). Car fixed, me happy that Espace runs great.

BUT after running faultlessly for a only one week (around 70 miles) the misfire has now returned!  I'm not a very mechanical minded person and haven't had a chance to check the new rotor arm for cracks, but assuming it has cracked again does anyone know what might be causing it?  Could the distributor be faulty? The rotor cap is also new by the way.

Many thanks.