The old round hole one has been pulled many years ago already which is why they offer this kit with the new squared axle end and the new free hub.
This then replaces the old round axle and its free hub.
The old free hubs will fit on the new axle but not vice versa.
I am certain there would be a significant number of people ready to buy FH-RE415 if they could get it.
That's the spare part number for the kit:
If you mean the combination of FH-BO001 and FH-BO015, that's different
The advantage of the old FH was that you could rebuild it completely whereas the new one won't give you access to the inner side's bearing (well it is not impossible but no shop I know of will actually to it) which nine out of ten will die first anyhow.
Either way, your FH can still be rebuild if it's the bearings that caught water. All it takes is pushing the alloy barrel to the side, push the top bearing out, remove the circlip that holds the inner bearing down and then pull or push that one out.
Then you put new bearings (2 x 6803 SKF with one rubber seal removed) in. In reverse order.