One thing that seems to happen to the airboxes fairly often, is that the bolts holding the airfilter foam and mesh inside of the airbox get tightened too much, splitting the plastic "ears" holding the imbedded nut, allowing the nut to turn. I think there's a tendency to tighten the h&!! out of everything on the bike to make sure that it doesn't vibrate loose. All four of them on my 95 model are split, and one nut was turning when I went to service the air filters today, preventing me from removing one of the foam filters.
I think I've come up with a fix for the problem, instead of the $56 for a new airbox. You can remove the airbox from the bike, and get the bolt out of the spinning nut by clamping onto the split plastic with a pair of pliers stuck through the hole in the back of the airbox. Then, put small hose clamps on the plastic "ears" to close the split for reinstallation of the foam filters. There's some photos here:
I haven't road-tested this repair yet, but I can tighten and loosen the bolts holding the filters now.