Peter check for wear on the hub ends of the shafts which can be caused by either a bearing or a seal. I went through about 10 axle shafts before I found a set that which were not too badly worn. Some have suggested a speedi-sleeve or a sweat weld to build up the groove but it won't work. People today will weld axles but those are not 50 year old ones.

1949 Chevy 1/2-Ton
"Sedgewick"
In the Gallery
1989 Caprice