I seriously doubt Nathan, or anyone, would be d-u-m-m enough to use any kind of Loctite on a bolt intended to be frequently removed. Maybe change that to "I would hope that..."
It's also possible that the bolt is Grade 8, but I doubt that's why it broke. The nut or bolt on an AC can be tightened down until the AC is a crushed ruin before you reach anything like the kind of strain the fastener would need to break. There's a huge amount of rubbery compression ahead of that, from the air filter between the housing plates.
I'd say it's just a flawed bolt that took all the vibration it could. I'd second using a good piece of all-thread and a nice decorative nut - I use a chrome washer and a chrome acorn nut on my long oval. If I press down a little on the lid, I can tighten it plenty much just with fingers.
An easy-out will likely pull the stub out with no problems. Steel bolt in cast aluminum = next to no retention torque to worry about.