Rex,
Heres the problem, NOT ENOUGH TORQUE....
Replace the axles and the hubs then give them a good 150 ft lbs of torque.
Been fixing these cars since the 79 year model was introduced.
Seen lots of ruined hubs and axle splines, always the same deal, insufficient
torque at the axle nuts. Use a new 056 050 500 cotter pin as well.
Good luck.
Norm.