diff noise


hi got a wining noise under my 4trak and little transmission oil leaking my mate thinks its the diff, also he thinks maybe a [or few] bearing are worn or broke,whats best thing to do change diff or axle or if possible get my diff repaired, 4track as done 70000miles engine an gear box is sound condition anybody out there can help also had few quotes on diff 220pounds to 420 pounds for diff many thanks MARK