Sorry to hear about the loss of your Zumo. I was in the second group, we ate first then went to the plant. It seemed that there was a fair amount of activity at the plant, trucks coming and going, people walking around. I can't imagine any rider doing this! My Zumo stayed on my bike during the whole event, in fact, I never took it off during the whole rally, just stayed on the Garmin mount, no security at all. I normally take it off, but at a BMW event, I did not bother. I guess I was lucky, if I was in the first group, I guess they would have gotten mine, it would have been easier for them!
Good Luck, I hope someone tries to get the unit serviced.