Wallace,
That is a good point and I had not thought of it. I just checked and they do make an extreme pressure and temperature version that they recommend for extreme shock applications. I do know that the concept is that the grease should not leave and the inner seal should keep them separated I have seen more without grease than with. One one hand I know good old EP Grease will work for quite a while but on the other hand I know that the Superlube won't harden up or mix with the diff lube. Sort of a tossup at this point.