Ah yes, forgot to mention that as well. I don't what the arrangement is on the Mighty Max, but on the Gen I Montero the breathers for the tranny/t-case are through the shifters. The rear diff has a breather that goes up into the frame and the front diff just has a breather with a check-valve that always seems to not work ideally. I routed mine with extended breathers up to the top of the engine bay.

If you get water in your gearboxes you'll want to change your fluid as soon as possible. Wheelbearings should probably be re-lubed as well. How often? I'd say do it more often than not.....eventually you'll see how well your bearings are sealed up and you can adjust your post-water-crossing maintenance schedule from there.