Alternator Pulley NUT Un-threaded itself

[BenzBid]

Alternator light has been on for the past year. Had a bad diode that was not converting all of the AC over to DC. Finally got around to putting in a refurb a few weeks ago.

Last weekend I was poking around under the hood and noticed that the long "nut" that threads onto the end of the alternator adjusting bolt was missing. I remember tightening that baby down with a 10mm and found it quite odd that it had un-threaded itself. I put a regular nut on there until I could get a replacement (still looking).

Today I notice this really odd clatter noise on the drive home. I pull over check the belts and such, all seems well. When I get home I take a closer look with a flashlight while the engine is running. The alternator pulley seems to have a very slight wobble. Turn off the engine and check the alternator and the bolt that holds the pulley on is missing?!

Kind of odd that both nuts have un-threaded don't you think? As my leaking oil and transmission pans will tell you I am one to over tighten and opposed to under . Should I have used loctite on the pulley bolt? Anyone else had this happen?