coil problem

[datdrift]

my car started misfireing, and after poping the bonnet there was a clicking coming from the coil. on closer inspection i could see it sparking where it had burnt through the rubber boot which goes round the ht lead. so i replaced it with a new one which seemed to solve the problem, but its started doing it again. is it just a case of replacing the coil or could there be another problem?
i know i have some spare coils, but i cant find them

[30psi]

I had that once. What is it arcing against after the rubber has broken through? I think mine was the air filter bracket adaptor or something. I think after time it just arcs its way through the rubber.

Would be worth checking to see if the plastic around the coil isn't cracked too