What causes the rear seal to walk out and how can I prevent it from happening again? Is there a superior seal out there that people are using compared to others on the market?

 

First observation is that if that is a static image. you have not travel for the axle moving vertically.

 

Not sure if zpg is saying the same thing, but it looks like the yoke is pushed in past its smooth machined surface and the rough surface it grabbing the seal.
In other words, the drive shaft is too long and contributing to the problem.