I wonder if that bolt loosened?

#1

Don’t wonder. Use something to mark bolts and nuts. http://www.aircraftspruce.com/catalog/cspages/f9002.php

#2

What’s funny to me is that we used Torque Seal at Walmart on the drain plugs of the oil change cars so we would be able to tell if the owner or another shop had messed with the plug since we did the oil change.

#3

I just use an old bottle of red touch up paint to mark my bolts.