The failure of the seal is not what caused the shaft/cup failure. It is the other way around. The cup and shaft start to heat up from friction caused by lack of lube and the heat destroys the seal.
This comes back to----- is the shaft/cup lubed with final drive fluid coming through the two holes in the cup or is it lubed by the grease installed at assembly?????
I know I wasn't putting enough grease in the pinion cup at assembly, because I weighed it last
time... it is time for a new tire... I'll see what's in there now soon...
Of course, all greases don't weigh the same amount, but "four quarters worth" is how
much grease the Honda manual calls for...

-Mike "the grease is in one of those creamer cups the people at work adulterate their coffee with"