found 14ff Maybe..

I might have found a 14ff out of a 2002 2500HD for cheap,the only thing is that it is a core axle,meaning it was traded at a used auto parts place for a good one.The axle has 4.10's and factory disc brakes but the guy says that there is something wrong inside the housing (gears,posi,etc...) should be no big deal since i will regear and detroit it anyway but what should i look for before i buy it????????????