I'm sorry to hear you're experiencing that. It's not right, for any make or model that a dealer not stand by their work up to a reasonable point, and it gets tricky when your independent guy finds something that appears to have been done incorrectly by the dealer, A: you've no way to prove someone else hasn't been in there since the dealer touched it and B: 400 hours is long time to be able to pin on the dealer. Imagine running a tractor around the clock for 16 days without issue and then it fails a few hours into day 17. It's really hard to pin something on them when it does that much work before it fails. The flip side, if you had let them do the work, there's a 95+% chance you'd have never known there was anything installed incorrectly the previous time, and I'm probably being generous on the 5% in their favor if they are in fact not the most ethical place. 

The other downside is that owning a McCormick is part of the risk itself I'm afraid, and I say that as an owner of one. For me, the cost difference between buying mine new vs one of the 3 most popular colors is what pushed me that direction, but the unavailability of being able to easily lookup parts and having no or few experienced service techs make it a risk. I've been lucky on mine, some 1,700 hrs and zero issues aside from one failure that I caused, but I would have had a little more peace of mind had I gone with something really red, green or blue.