It probably flew off his shelf after 11 years. But just as well, because those factory air filter boxes are known to be problematic and can dust the engine if not watched closely. I believe the only recall my '96 ever had was for that box, and all they did was replace some plastic hold-down rods with metal ones, as I recall. I never really trusted it because it is a box, which means you don't know what's happening inside. I believe those OBS air boxes are known to warp or otherwise get a bit out of shape, and it doesn't take much of a gap to let harmful dirt bypass the filter inside.
I'd suggest you do what I and a lot of others have done: replace the factory box with a Tymar system that discards the box in favor of a large truck filter which allows you to better see if there are any problems with it. It's a much simpler approach that is extremely effective.
