Don't go too hard on the dealers. They're only human.
I had a 3176 in a 140H with what sounds like the same problem; an intermittent fluttering missfire under heavy load. Spent hours with ET trying to pinpoint the bad injector but no luck. As the customer didn't want to spring for six reman injectors, and it wasn't causing him any operational problems, we left it.
It gradually got worse and six months later we could pin it down to #1.
I suppose the takeaway is, if it only sounds broke, don't fix it.