I swap back and forth on my 2 chunks..the 489-3.91sg has the block,then 742-3.23 open has no block.

I run the axle seals and I have run with out them a few yrs now with out seal... just the o-ring on the green bearing.. so far it has not leaked past o-ring or thru the sealed bearing.

it is better to run them for added protection against leaks but I boogerd the last set with a BFH and running without them till next gear swap.