I understand it is possible for the hose into the crankcase to break off/down into the crankcase...have to pull the pan to get it out. don't fool with it.
The box/O rings are a dealer item for all practical purposes. If you can blow through the hoses, don't fool with the box. The nipples are generally the areas/restricted where stuff accumulates and plugs up. Use a drill rotated by hand to clear the nipples.

Lastly, sometimes excessive crankcase pressure is clearly due to worn rings or bad oil seals. Do a compression check and be sure you have good compression (squirt oil in the spark plug hole and see if compression goes up by more than 5psi....if so, worn/poorly seating rings). Should have no more than 10psi variation among cylinders. Can also blow compressed air through spark plug hole with proper adapter...see if valves are leaking or air is blowing by piston rings (air at carb/throttle body indicates intake valve leak, air noise at exhaust pipe indicates exhaust valve leak, air noise at oil filler hole indicates blowby piston rings).