I have a 97 xj sport, pretty sure somewhere in its life it had a hard front end hit. Blower has never worked well since i got it 3 years ago. Earlier this year it started losing all of its air moving capacity, dispite the blower motor being strong. Pulled the radio and glanced in. Box had been patched before in several places. Now coming apart. Would like to replace with a new box/heater core/evap, but cant seem to locate one. Is used my only option?