Has to come out . Best way is to turn the tail shaft and press out the pin holding the reverse gear. . You may get lucky and not rip the gasket. But if it was mine I would Tear it down reseal it and take a look inside. Unless it was just rebuilt.
Not trying to pick a fight here, but are you suggesting to pull the tail with the main box still on the BH? I mean I guess that is doable, altho I've never tried it. It would sure save time!
But how the heck do you remove the idler-pin? if you can't beat it out from the front. Did you make a tool? I'd be interested to see how that tool works with the cluster still in there..
Just trying to learn something new