I wound up sending my amp in for an out-of-warranty repair. They told me to send in the entire sub, box and all. I sent them my ratty old, dented, beat-up sub box. They promptly sent back the "repaired" unit. It was shiny-new with no dents or dings -- absolutely pristine. And it works great!
I'm a happy camper, although I'd have been *happier* if the fix was something obvious enough that I could have done it myself.