I think the only way to really stop this is to install one of the seals that is made to fit where the torque tube connects to the axle center section. This is an aftermarket part made to address this issue.
Here is one type, but there are other I believe.
http://www.seabrighthotrods.com/?p=522
https://www.jalopyjournal.com/forum/...stion.1057458/