Get your complete assembly from Steve at Tousley Ford (he's cheapest amongst our parts sources, at least for THAT particular part. Him and Bill Jenkins are both excellent people and I wouldn't hesitate to give my money to either of them!)
His contact info is in the Duratec Maintenance FAQ.
Incorrect pressing procedure, incorrect axle ut (AKA Locking spindle nut) torque (208-214 FOOT pounds

) and a scarred or worn hub (from a bad bearing spinning and being left unattended for too long, thus not a tight fit anymore) will all contribute to VERY quick failures.