[Sans Peur]

I would bet on the coil going bad. Especially with a crack around it. Coils will work for a bit and then once they get hot will break down and stop working. I had a customers forklift doing the same thing and one of my technicians put 8 hours and quite a few hundred dollars in parts trying to fix it awhile back. I asked him if he had put a spark tester on it and once we did the problem was obvious. Replaced the coil and everything was perfect again.

Always start with the simple things first, usually that's where it will be.