I decided to do some searching and found this:
http://nicoclub.com/zerothread?id=90753
I'm NOT a tech, but since you haven't gotten any good answers yet, I decided to see what I could find using "firing" in the search field here. It seems reasonable to think that it's an electrical issue - a missed reconnection when they replaced the stuff - bad ground, sumpin like that. My guess is that they need to do some work with a multimeter.
Maybe a waste of time, but I'm impressed at what you can learn from searching old posts.